Download SLAC -62 UC -28, Particle Accelerators and High

SLAC -62 UC -28, Particle Accelerators and High-Voltage Machines TID-4500 (48th Ed. ) THE STORY OF STANFORD’S TWO-MILE-LONG ACCELERATOR May 1966 by Douglas Wm. Dupen Technical Report Prepared Contract r Under AT(04-3)AOO for the USAEC San Francisco Operations Office 1 Printed in USA. Price $4.00. -4vailable from the Clearinghouse for Federal Scientific and Technical Information (CFSTI ), National Bureau of Standards, U. S. Department of Commerce, Springfield, Virginia. “L -*,-wmppwwmm-m _--- Il^.L_ s&trr2..* -’-.1’.--- _ .-. .^. .-- . --.. e”-.------r---Y-.--.tXf~~<.*be.whs-(T ,V” _..j.nkUi -.,w.mI “.... - ii - TABLEOFCONTENTS Page ............................. Introduction I. The Expansion of Scientific II. 1 IV. Historical Electrostatic A. Early Accelerators: B. The First Big Step: The Cyclotron C. The First High Energy Electrons: F. Higher Energy Protons: 11 Acceleration ........ 11 ............... 13 The Betatron ........ 17 ................... D. Reaching for Higher Energies Higher Energy Electrons: 8 .............. Development of Accelerators E. 5 ................... Ways and Means of Observation III. .............. Investigation The Electron 19 . . . . . 20 . . . , . . . 21 Synchrotron The Synchrocyclotron ..................... G. The Proton Synchrotron 23 The Development of Alternating H. .Raising the Limits: Gradient Accelerators ; .................... I. V. VI. ............................ The Future Linear 26 ......................... Accelerators Development of the Electron Resonant Cavity Principle: B. The Traveling C. The First D. The Klystron E. The Next Machine: F. The Mark III ........................... . “..“, .--_. . .__-,*__ e-e .--m 37 ....................... Tube m--u__-. 36 The Mark I ............ Stanford Machine: The Mark II .-- 40 ................ and Accelerator _ 45 . 46 Development ..... 53 Machine ............ The Beginnings of the Two-Mile _ 34 ........ .................. - .. 34 .......... The %humbatron”. Wave Concept G. Other Stanford Klystron r 28 Linear Accelerator A. H. 24 54 ... 111 - . v--F , . ,. . ..I. . , _. *. b...CI, .s.js.aw.v e.(r-, ,, Page VII. Radiation VIII. The Site. IX. x. XI. ............... .................. Housing Construction System ....................... The Acceleration Auxiliary .......................... Systems 59 66 ............................... Accelerator 70 82 89 ............................. A. Injection B. The High Power Klystron C. The High Voltage Modulator D. Trigger E. Drive System F. Phasing System ......................... 96 G. Beam Guidance ......................... 97 H. XII. Shielding for the Accelerator Vacuum System J. Temperature K. Electrical L. Instrumentation III. . :, . ._ .................. Control System System .................. ........................ and Control 91 95 95 96 ......................... Using the Accelerator II. ................... .......................... I. I. .................... ......................... System. Support-and Alignment Appendices: 89 ................... ....................... 98 101 103 105 107 108 ................................ SLAC Chronology. ........................ Specifications ............ ............... Accelerators 115 General SLAC Accelerator 117 Energy Particle 119 High Bibliography. 121 ............................... 127 Index .................................... - iv - * LIST OF FIGURES page Aerial 1. view of Stanford’s new two-mile-long accelerator the 20-GeV linear accelerator structures comprising 2 . . . 3 4. Sketch of the accelerator 5. The nucleus of the atom appears to be the source of dozens 6. Comparison 7. Negatively structures . . . . . . . Cutaway drawing of the two two-mile-long of little-understood site, just west of the campus proper “elementary 7 . . . . . . . . . . . . . . . 9 are repulsed by the like charge from the negative side of a power supply and attracted opposite charge of the other side. _ Passing through a magnetic field, to change direction . . . . . . . . . . . . . . . . a charged particle beam starting The principle of the Betatron is similar in the center of to ordinary transformer 11. Principle 21 12. Simplified diagram of the Wideroe type of linear accelerator . . . . 29 13. Simplified diagram of the Alvarez . . . . 32 14. Single resonant cavity accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 of operation Multiple of a Synchrotron . . . . . . . . . . . . . . type of linear accelerator using the Rhumbatron resonant cavity accelerator . . . . . . . . . . . . . . . -v- -.x. . 15 18 15. - 13 action (a) . . . . . . . . , . . . . . . . . . . . . . . . . . . principle - 12 is made . . . . . . . . . . . . . . . . . . . . . . . . . . a Cyclotron 10. by the in a curved path (top) . . . . . . . . . . . . . The spiral pattern of a particle 9. * . . . . . . . . . . . . particles” of four “microscopes” charged electrons 2 . . . . . . . . . . . . . . . . . . 3. 8. 1 . . . . . . . . . . . . . . . . . . . . . . . . . . Phantom drawing of the two-mile-long 2. linear electron NW” . .._ Y L_.. ,. .,I m.IIC11-l--m-4w-s _II*.. -I-Yy”,w.Tv /~~I~ “.-, ~-~*ni-,~rn~nrw~~-.~~,..~. -..--- _ ” ., -.__- . .-.“..---.__---~-_-.~cII ./ .,-..lr.-dm. 36 LIST OF FIGURES - Continued Page 16. Simplified 17. Cutaway drawing showing internal 18. presentation of the traveling wave principle configuration . . . . . . 38 of . . . . 38 W. Kennedy and W. Hansen . . . 39 . . . . . . . . . . . . . . . . . 41 . . . . . . . . . . . . . . . 43 . . . . . . . . . . . . . . 48 accelerating waveguide showing three cavity forming The original Mark I electron linear accelerator disks photographed in the Stanford quadrangle and being held by, left to right, S. Kaisel, C. Carlson, 19. Principles of radar operation 20. Principle 21. Schematic and plan view of Mark III 22. The first of klystron amplification sections of the Mark III accelerator, in the opposite direction injector) 23. 24. to beam motion (looking toward the -. . . . . . . . “. . . -. . . . . . . . . . . . . . . . The Mark III after replacement in 1964 of its acceleration earth shield 53 levels outside the accelerator’s . . . . . . . . . . . . . . . . . . . . . . . . . 63 . . . . . . . 67 . . . . . . . . . . . . . . . . . . . . . . . . . 72 25. Location 26. Typical cross sections of Accelerator 27. 49 sections . . . . . . . . . . . . . . . . . . . . . . . . . . Calculated radiation earthwork as seen looking of the Stanford Linear Accelerator The two-mile-long cut-and-fill Housing and in mid-1964, toward the Pacific Ocean from the initial the two target buildings Center looking west excavations for . . . . . . . , , . . . . . . . . . . . 28. Sketch of the sub-slab laid before Housing construction 29 Sketch of the Housing under construction - vi - in the trench 73 began . . . 74 . . . . . 75 LIST OF FIGURES - Continued 30. The first few sections of Accelerator pea-gravel . back-fill 31. Accelerator 1 covering the protective Housing construction western portions Housing with the Celotex sheets . . . . 76 continued eastward while . . . . 77 . . . . . 77 were being covered with compacted fill 32. Sketch of the completed fill over the Housing, showing the top of several of the penetrations leading to the Housing 33. The western end of the completed Accelerator Housing with 25 feet of compacted earth above it and construction of the Klystron 34. The framing Gallery begun of the Klystron 35. Sketch of the Klystron Gallery 79 . . . . . , . . 79 Gallery as seen from the injector . . . . . :. .. -; . , . . . . . . . . . . . . . . . . . . 37. Cutaway sketch of the Klystron Housing showing interconnection the man accessways Gallery and Accelerator penetrations and one of 81 . . . . . . . . 82 accelerator stages 39. Diagram of the present klystron-to-accelerator configuration (Stage I) and of the possible future configuration I . diameter, 41. One lo-foot 80 . . . . . . . . . . . . . . . . . . . . . . . . 38. Two of the 240 forty-foot-long 40. Copper cylinders 78 . . . . . . . . . . . . . . . . Gallery under construction 36. The complete Klystron drwestend . . . . . . . . . . . . . . . . . . ? . . . . 84 . . . . . . . . . . 84 . (Stage II) and disks making up the four-inch- two-mile-long accelerator structure section of the accelerator pipe showing the input and output rf couplers at each end and the small center-fed pipes forming the accelerator temperature - vii - control jacket . . . . 85 LIST OF FIGURES - Continued Page 42. A completed 40-foot module on the transporting to be taken to the Housing for installation 43. The interior of the Accelerator of the accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . diagram of the injector, 91 . . . 92 . . 94 . . . . . . . . . . . . . . . . 94 45. Qltaway drawing of the SLAC high power klystron 46. Five of the high power klystrons, by four different The interior of the Klystron 48. Each 40-foot-long showing major components. accelerator girder is loosely coupled to . . . . . . . . . . . 99 girder rests upon three supports . . . . . . . . . . . . . . . . . . 99 One end of each 40-foot-long adjustable worm-screw 50. A retractable Fresnel zone plate target is housed within each 40-foot-long girder to intercept and provide alignment indication 51. the laser light beam . . . . . . . . . . . . . . . . . . 100 Typical block diagram of one of the 70 closed-loop lating water systems for the accelerator 52. i 53. as companies and by SLAC itself the next with a flexible bellows arrangement 49. amplifier ready for installation, Gallery 88 . . Simplified 47. 88 Housing after installation 44. manufactured rig ready One of the pole structures recircu- and its components . . . 104 in the SIAC high voltage transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . 106 The research end of the accelerator - .. . Vlll . . . . . . . . . . . . . . . . 108 - . . PREFACE Y The two-mile-long electron linear accelerator The development of this type of accelerator been carried out primarily is barely three decades old and has at Stanford University. this new machine was done with great dispatch. this exciting scientific sional journals, notebooks, at Stanford is now a reality. The physical realization of The details of the story behind tool exist only in bits and pieces: in specialized profes- in government in internal reports, in consultants’ findings, memoranda, in laboratory and, in some areas, only in the memories of members of the staff. The following pages present the story of this accelerator, of the development of machines for high energy physics, the appearance and evolvement of traveling wave electron linear accelerators, eering of this machine, the construction to geological considerations, calculations and the use of the machine in elementary of the facility the background the design and engin- with particular and planning for radiation particle this material documents. existed previously but only in widely scattered, These, which are drawn upon heavily, i * and are gratefully acknowledged. -ix- containment, physics research. Many sources have been drawn from in developing this narrative. . attention Much of often one-of-a-kind, are listed in the Bibliography . I. INTRODUCTION Occupying 480 acres of Stanford University’s electron linear accelerator “academic lands,” a 20-GeV extends for two miles from west to east (Fig. +‘--, -.-., 1). _ “I . ! __/ ,-’ _’ , /” &+ , / &. -: i$;;- P. I _.d”-. ‘kc : .--ys i ke.’ &......“= ::., Y . - - _ I’ t FIG. l--Aerial linear On this narrow Crete tunnel, strip of land, Stanford has constructed 25 feet underground. cross -section, Electrons proper, Parallel electron This structure, a copper cylinder its two-mile approximately length, having been accel- volts of energy. a 17-foot-high called the “klystron and devices for providing Integration 10 feet by 11 feet in internal to this lO,OOO-foot tunnel and directly another 10, OOO-foot long structure, a lO,OOO-foot long con- are injected into the west end of this small and exit from it, after traveling erated to as much as 20 billion shed. This tunnel, houses the accelerator four inches in diameter. cylinder vi& of Stanford’s new two-mile-long electron accelerator. for the acceleration by 30-foot-wide sheet ste&l gallery, ” contains all the components of the subterranean of the functions of these two structures - 1 - above it at ground level is is performed electron beam. via vertical holes (“penetrations”) in the separating earth fill. 20 feet apart along the entire length, permit ment in the upper structure (Figs. These penetrations, interconnection and the accelerator between the equip- tube in the lower structure 2 and 3). FIG. 2--Phantom drawing of the two 2-mile-long structures 20 -GeV linear accelerator. comprising the I ACCELERATOR PIPE 2 ADJUSTAGLE SUPPORTS 3 WAVEGUIDE I KLYSTRON TUBE i MODULATOR j INSTRUMENT PANEIS I.1 FIG. 3--Cutaway drawing of the two 2-mile-long -2- usually structures. At the exit (east) end of the accelerator, an underground “beam switchyard” bending and directing where research which contains magnets and other devices for the accelerated electron beam into selected “target with the beam is carried out. areas” In this “end station area” are two buildings. ” Two target buildings were planned in order to be very large “target able (1) to be preparing one experiment in one target building while the beam is (2) to “share” the beam if desired by directing in use in the other, one target building and part of it to the other, target buildings another thousand feet is used up by differently part of it to one and (3) to design and equip the two for the two major classes of experiments performed with this kind of machine. Also near the east end of the accelerator which provide office, the staff working laboratory, are the dozen or so large buildings and shop space for the thousand members for Stanford University operating of the Stanford Linear Acceler- ator Center (Fig. 4). --- ---- --~----- - . AL C~O&IECTION FIG. 4- Sketch of the accelerator site, just west of the campus proper. - 3 - -.-._l___ ..-.--_I- _ ----se-. I . .---. - ._____ - -..-e ____-_.. - L.----lew.,v- ---w . . I The Stanford Linear Accelerator constructed, and operated by Stanford University Atomic Energy Commission. project in September 1961. Trustees and the Atomic under contract A contract latest and most esoteric with the U. S. Energy Commission in April and installation costing $114,000,000 of a continually serve the needs of the relatively the was signed between the Stanford Board of 1962. Ground breaking were essentially Research with the beam began in November This accelerator, designed, The Congress of the United States authorized took place in July 1962. Construction in mid-1966. Center (SLAC) is a national facility completed of that year. to design and build, is one of the growing family of gigantic devices to young new science called “High Energy Physics. ” - i -4 ~.s’“*L1*rgpllrlffnr- *.--~~“~~.“~“I~-~“:~l---~~.~~-‘,~-”-~---^- - ------.~f- - . . . ..__.._ x.e_y.-~ --.I ..----..-_^ ,Ta --.--. ...A”c?.*w~~~“-~-l- .v ‘ .“-. . P II. THE EXPANSION OF SCIENTIFIC The exploration of the physical universe has proceeded in two directions, opposite but not unconnected. Our knowledge has expanded to encompass phenomena which take place on a scale vastly different the astronomically experience, Physicists INVESTIGATION* from that of our immediate large and the submicroscopically now comprehend not only the structure our own and other galaxies, the curvature of stars, objects to molecules; posed; the internal structure clei; the nucleus itself, them together; itself, complicated, of the atom with its electrons out of whose interactions has varied enormously has become more detailed and precise; of modern physics. thereafter particles” . We are peeling an onion and combinations particles. unexpected, our whole ” This is a term as our view of the physical universe the changes in its meaning mirror the In the time of Newton and for almost a century the connection between the structures understood and there were, .I around nu- of the inside of the proton seems to be formed are called “elementary history orbiting each layer uncovering in a sense another universe; . _ and-- as we understand more-- strangely beautiful. whose significance scale: from made of protons and neutrons and the forces which bind and lately even something of a picture The basic particles universe and smaller then to the atoms of which the molecules are com- complex and containing yet other particles. layer by layer, the motion of of space, the possible ways in which our universe has evolved, but also matter on a smaller familiar small. of different in this view of our world, as there were kinds of matter: water, materials was not as many “elementary salt, oxygen, iron, quartz, etc. , 4 Much of the material in this section and the following section appeared in a report originally prepared by a special panel on high energy accelerator physics in 1959 for the purpose of acquainting Congressmen with this field of science in preparation for the U. S. Congress’ consideration of supporting the construction of the two-mile accelerator. -5- npIcI4rmRpI’..., -llll---.-” I. . 7, *. * ** -lm’.,l*u. --__c. n-,.~.,*,,~~~~uQnr~~.Npr~anu-rr.~.~~-~~=o- _.--. -,-“‘7--’ I . “ll--e”““--,-r” . ---- .-, -,.-““cI,~..~.-.~~~.,’ The uncovering an immense number. the nineteenth century, of a finer structure revealed that all matter, to matter, mainly with all its different in sorts of molecules, was composed of fewer than 100 kinds of atoms; these became the elementary particles of last century’s physicists. Shortly before the first world war we had our first appeared as a very small core, the nucleus, trons whose configuration the atom. open. surrounded and number determined by one or more elec- the chemical properties of More than three decades ago the tiny nuclei themselves were split Observations were difficult, fuzzy, all nuclei were composed of combinations approximate, approximately but clearly distances, 100 atoms were indeed not truly the elementary but were themselves showed that And so, as of protons and neutrons. we peeled our onion and looked to more infinitesimal universe, look inside the atom. It we saw that our particles made up of a very few kinds: protons, of our neutrons, electrons. Rut the view that these three”particles particles might be the ultimate of our universe has been emphatically vances in theoretical understanding that the appearance of our universe and experimental when looked at with instruments ily fine detail, revealed a substructure involving Remarkable ad- technique have revealed is not nearly so simple. tary particles, ticles (see Fig. 5). destroyed. elementary Various elemen- which can resolve extrordinara host of new and strange par- Our onion has more layers. High Energy Physics is the exploration cerned with these phenomena, of this subatomic world. remote from our immediate and familiar It is consur- roundings . High Energy Physics research proceeds, not with any view toward specific useful application, for its own sake. but by pursuing discovery very heart of modern physics, understand and the product of many centuries our universe. -6- It is the of effort to .“-3.. FIG. 5--The nucleus of the atom appears to be the source of dozens of little -understood “elementary particles. ” W e cannot know what will be discovered from deeper probings of the subatomic world. Our only guide is past experience, that nature often turns out to be remarkably Such pure research, plishment, different by curiosity from any expectation. and the satisfaction of accom- has given us knowledge and understanding of many of the phenomena of our world. with larger stimulated and here the lesson is evident The practical accelerators numerous and fantastic. results that must derive from continued exploration cannot be guessed. If the past is a guide they will be The one thing that we have learned to expect from nature is to be surprised. ” High energy physics is one of the leading intellectual developments of our age. It is not only very exciting but experimentation in this field will probably lead to some of the most important theoretical and perhaps then the most practical developments of our age.” 1 1 Glenn T. Seaborg, Chariman, U. S. Atomic Energy Commission -7- .-- .__---=. *L-.--w. C. ,v*. WW III. WAYS AND MEANS OF OBSERVATION With our eyes we can distinguish thousandths of an inch. smaller A microscope scale than that. objects whose size is as small as threeis used in order to see detail on a much But the nature of visible light limits detail that can be observed even with a microscope. ment confirms Theory predicts that with even the most perfect optical instrument sible to see anything smaller than about ten-millionths times the radius of an atom, a hundred million so in the conventional hope to do so. and experi- of an inch, a thousand times as large as a nucleus. of atomic and nuclear particles different of it is not pos- sense we cannot see an atom or a nucleus, The exploration ferent type of vision, And nor can we ever demands a dif- kinds of instruments. One way to try to see atomic particles shorter the sharpness than that of normal visible light. is to use light of wavelength much Such short-wavelength forms of lights are emitted only by sources that can impart a great deal of energy to a single light wave; the higher the energy, the shorter the wavelength and the more clearly we can see. However, short-wavelength to nuclear dimensions atomic particles nucleus, light is not the only tool used to explore down and below, nor is it even the main one. itself can be used, like a beam of light, and beyond. Particles of matter--electrons, --behave in many phenomena exactly like light waves. A beam of sub- to probe the atom, the protons, They,too, and all the rest have associated with their motion a wavelength which decreases as their energy increases. as with light, this wavelength limits of particles. Thus an electron microscope, stead of a beam of visible light, whose wavelength is smaller with the electron energy (Fig. And, the detail that can be examined with a beam which uses an electron beam in- defines more detail because it utilizes than that of visible light. 6). -8- The definition electrons increases . “LIGHT” USED - OPTICAL MICROSCOPE ELECTRON M ICROSCOPE VISIBLE LIGHT ELECTRONS 50,000 2eV ENERGY WAVELENGTH SMALLEST OBJECT “SEEN” STANFORD MARK III ACCELERATOR STAN FORD TWO-MILE ACCELERATOR ELECTRONS ELECTRONS I BeV eV 20 BeV lo-l4 cm TO 10-15cm IOw5cm IOwgcm 10vi3cm MILLIONS OF ATOMS THOUSANDS OF ATOMS NUCLEUS OF THE ATOM PARTICLES INSIDE THE NUCLEUS $ TYPICAL OBJECT OF STUDY -4 10e3cm LIVING VIRUS CELL FIG. 6--Comparison Of course, --I -4 IO-‘*cm L ATOMIC NUCLEUS IO%m of four “microscopes. a “look” with a beam of electrons ent from the kinds obtained with visible light. differ Beams of high-energy differ- protons The various views universe. It is figuratively which they give. our landscape with a variety of cameras, the houses, another the trees, The familiar 473-2-B ” kinds of beams are all equally valid descriptions in the precise information photographed PROTON gives a type of picture furnish still another view of our submicroscopic obtained by using different IOwi3cm I+- but as if we had one of which films only a third the streets. objects around us are unaltered when we turn on a light in order to see them; the molecules and the atoms of a cube of sugar or a glass of water are. not appreciably . disturbed the energy of the light or particle see at atomic dimensions, However, by visible light. if we increase beam in order to decrease its wavelength and then the energetic light waves or particles shake up the atoms and often break them up into their constituent seriously electrons and -9- -- -.q---ymp rCp--P-~“*e-w-~ -- __-.-- ----- --- -._. .- ..- -- _..-,. -- ..I _. -. ..,. -. -.. ...)rz.rm--*“-- nuclei. Beams with a wavelength short enough to probe a nucleus also have high enough energy to split the nucleus apart by knocking out the tightly bound protons and neutrons of which it is made. In this way a sufficiently system that is observed. (particles) striking A detailed observation high-energy disturbs various new particles It offers a partial view of the target’s are the beams of high-energy vices to detect these particles upon the great particle has two assoc - interior, and it frees which may usually exist only within a struck particle. Thus the main tools of the physicist Our understanding the beam of light a proton or neutron or any other target particle iated consequences. tons and impart violently who explores the subatomic universe particles which are his light, and the various de- which are his eyes. of the ultimate structure accelerators, of matter which take low-energy and energy depends electrons or pro- to them the enormous energy necessary to “see” to distances which are to the thickness of a sheet of paper as the thickness of a sheet of paper - is to the distance to the moon. - 10 - ~--~-v-*--F-~.* ‘~.. ~..uru-r..‘~~.~:.*~~,L.IY,.,),,,11.9.~i- _I --.I- %.I ‘I..c “.wx”..-.lw. 3 ‘*--a*, .” _ . _ ” _ -.-,-, a .---1-w ..~,,. -~--a---L “0, . ..r.- .,., _ . -“IL- IV. HISTORICAL DEVELOPMENT Types of subatomic particles are electrons, of hydrogen, . particles” ’ 6 titles, A. protons, commonly used to form beams in accelerators The last three, deuterons , and alpha particles. deuterium , and helium atoms respectively, and are positively Early Accelerators: charged par- Acceleration half of this century, men began to develop deso that controlled using the beams as investigatory machines caused whatever particles potential field. are classed as “heavy are negatively beams of such subatomic particles ments could be performed nuclei than nuclei. Electrostatic Around the middle of the first vices to accelerate Electrons charged. external to and much lighter the particle OF ACCELERATORS were to be accelerated The higher the voltage of this potential tools. experi- These early to pass through a field, the more energy beam acquired and the more useful it became. Energies of particle beams are measured in units called “electron (eV). Thus if an electron passes through a potential field of 500 volts, acquire an energy of 500 electron volts (500 eV). If a proton traverses volt potential field, volts” it will a 10, OOO- it acquires an energy of 10,000 electron volts (10 keV). Beam energies of these magnitudes were easily achieved in these early “electrostatic”type accelerators Power supplies to provide the necessary voltages (see Fig. 7). for higher energies than this were not feasible to build. To reach higher energies, allow . a particle Another technique is to charge up several high volt- each to the maximum then to discharge these capacitors a particle One was to beam to pass through several such potential fields in succession, gaining energy in each step. age capacitors several techniques were developed. voltage of the available power supply and all in series across an accelerator beam is injected at one end. The resultant - 11 - lube while energy then is proportional : POWER SUPPLY . - + ELECTRON --me-----) I-. . POSITIVE ELECTRODE NEGATIVE ELECTRODE 493-7-A FIG. 7--Negatively charged elec trons are repulsed by the like charge from the negative s ide of a power supply and attracted by the opposite charge of the other s ide. In moving through the voltage field, the elec tron gains energy. Elec trostatic accelerator development concentrated on the design of various k inds of power supplies to provide higher and higher voltages and consequently higher and higher energies. : 1 to the sum of the voltages on all the‘capacitors . the “Cockroft-W alton day, generating generator” This las t technique is the basis of type of accelerator. Such machines are in use to- beam energies as high as several million Still another technique, elec tron volts (MeV). developed by R. Van de Graaff in the early thirties , is to take the charge from a power supply and deposit it on a moving pulley which carries the charge to a large sphere, without arcing. a sphere smooth enough to retain the charge By doing this continually consequently high voltage, for some time, is built up on the sphere. beam then enter an accelerator I : i i : i Van de Graaff generator IO MeV. By operating The partic les and to form the tube at one end at ground voltage and are attracted by the high voltage on the sphere a dis tance away. / a very huge charge, type accelerators Beams generated in present have reached energies as high as several hydrogen ion Van de Graaffs in tandem and by - 12 - , alternating stripping B. the charge of the accelerated of electrons, The First particles by successive addition and even higher energies are achievable. Big Step: The Cyclotron Again, back in the early thirties, of having a beam of particles tential fields in succession. several people were working with the idea traverse a row of several relatively Pure physical ties of this technique until E. 0. Lawrence low voltage po- size and expense limited at the University the possibili- of California conceived the idea of causing the beam to move circularly and to return over and over again, alternating Thus was born the Cyclotron. The principle voltage fields. to and re-traverse, on which this design was based is that any charged particle, passing through the magnetic field between the poles of a magnet, change direction in a curved path (see Fig. 8). is made to With a large electromagnet of APPROACH I NG CHARGED PARTICLE FIG. 8--Passing through a magnetic field, a charged particle is made to change direction in a curved path (top). If the magnetic field is strong enough, the curved path will be tight enough to cause continuous circulation. - 13 - -, -I-w ” s-w p--w.“wy,-wnQ-----. .-- _... -.‘- ._..- -_-_ __ -_I._ ..^.. . ..-w”rs.a.qvr*nnrr---.weaT-.O sufficient magnetic strength, particles passing between its poles and into the magnetic field are curved in direction themselves and continue to circulate was to have particles , never leaving the field. The total energy the particles to the number of circular In the device that materialized pass through two voltage fields, Lawrence’s idea once, acquiring Then when the particles trips the particles from this thinking, energy, took. the particles One voltage field is the voltage on the diameter have completed a half-turn opposite side, they are again accelerated. actually After the particles of the circle. high would achieve would one during each half-turn. set up along a complete diameter this diameter back on do just that but to pass through a pair of alternating voltage fields with each turn. then be proportional so much that they actually circle pass across is reversed. to cross the diameter So that the particles at the do not feel the presence of these voltages while they are moving from one crossing point to the other, they are contained during their semi-circular shielding them. from. the accelerating Practically, movement in an enclosure voltage difference. this is done by building two devices in the shape of the letter “dee. ” It is as if an empty tuna fish can were sawed in half from top to bottom, forming two dee -shaped cavities. cept that a little These two dees are then put back together space is left between them. This doubledee arrangement exis then set between the poles of a magnet. If charged particles one of the dees and are started moving, they will move in a curved path until they reach the point of exiting from the dee. A high voltage is placed across the dees of such polarity accelerated that as the particles this time, inter-dee leave one dee and enter the other, and increase in energy. until they have made a half-circle The particles and prepare the particles they are then continue in their path to exit from the second dee. the voltage across the dees has been reversed transit, are placed inside are again accelerated. By so that on this second Each time the particles - 14 - up--..: ----,, yII --IIX _v--m+.a, .“.X”$ mr- %vs-r”m*“r _____-..-.,-, ^ _..?,-.. ,r,,...~.nz..,$..~.a”~ ._... --P”w-..---~--. --ST.“-- - _.. ._. . -_- _ _I II_ *. m-e. ~,.s.ee~-w,.w~‘~‘~ . complete another semi-circle dees is reversed and pass between the dees, the voltage across the so that acceleration The continual reversal of voltage polarity two dees to the two output terminals generator continues and energy produces an alternating course increase in velocity, by connecting the generator. This rf voltage of a very high, constant frequency. constant frequency of voltage alternation effects which cancel each other. is accomplished of a radio-frequency builds up. continually First, traveling A can be used because of two opposite as the particles gain energy they of faster in each half-turn. However, this same increase in energy makes it harder for the magnetic field to curve the trajectory of the particles so that each half-turn than the previous one. the larger semi-circle, moving faster. regardless is a semi-circle This longer path the particles of larger must follow, because of is compensated for by the fact that the particles Thus the time to complete each half-turn of the amount of energy the particles radius are is always the same, have been given. This constant enlarging of the circular path means then that the particles . _ actually follow a course which is much like a spiral (Fig. 9). The particles are FIG. g--The spiral pattern of a particle beam starting in the center of a Cyclotron. - 15 - started in the very center of the apparatus and are attracted has the appropriate to whichever In this first dee, the particles voltage polarity. dee begin to turn, Then they cross the gap and enter the other dee, having gained some energy. The turn in the second dee is a wider semi-circle in- than in the first. Upon reentry to the first dee, the energy has been again increased by the traversal and the semi-circle the periphery is larger Finally, again. of the dees , the particles when the path has spiraled out to are extracted from the Cyclotron directed to a target in an experimental area. (This extraction the magnetic field at a point on the edge of a dee be slightly Then an electrostatic degree of turn is reduced. of the gap and is done by having reduced so that the deflection plate attracts the beam toward the desired target. ) There is a limit, clotron. This limit increases however, to how high an energy can be achieved in a Cy- is set by effects due to relativity. in energy, there is also a proportional As any moving particle increase (which takes place at the e.xpen_seof the desired velocity that as higher energies are achieved, is no longer sufficient semi-circular path. increase)means the rate of increase of velocity the same as the rate of increase of energy. half-turn This mass increase in mass. is no longer The increase in velocity with each to compensate for the increased radius of the Thus the particles begin to fall behind the constant rate of voltage change on the dees so that they no longer cross the gap at the right time. Eventually they would fall so far behind that they would actually be decelerated. In the case of the “heavy particles, accelerated particles ” this effect is not significant reach energies above about 20 MeV. beam energy is very useful. Cyclotrons today, accelerating deuterons , alpha particles, protons, But the extremely trons can be accelerated until the This magnitude of of energies in this range are in use etc. small mass of the electron and the ease with which electo high velocities mean that this effect would limit the - 16 - ~n-l-w-%.-c.F ‘7 --~-~~~~,~ ‘I i>*-v* __-_ I__y-I-v”T.M-..-.~ ‘S*WW--MI’%*- ,~p..‘“V.-..X,.r _ _ ,_ - _-. /.- _.:- ,., -.--ssY-.-.-.-----~-, _,, ,s,c,:.. .#myp .“.I.‘, .-b~--*.~, acceleration of electrons this reason the first in Cyclotrons to only a few hundred electron volts. attempts at acceleration those achievable in electrostatic of electrons accelerators For to energies higher than had to take an entirely different path. C. The First High Energy Electrons: This different electron path eventually led to the Betatron, accelerator, the University The Betatron the first of Illinois. one of which was built in 1940 by D. W. Kerst at The principle of operation to the action that takes place in an electrical electric current lines of force is sent through a primary (flux) around the coil. lies within these flux lines. in intensity, a similar increased, creases (Fig. A secondary coil, This current an sets up adjacent to the primary, in the primary is caused to vary This change of flux “induces” If the current to flow in the secondary coil. in the primary is and the electron flow in the secondary in- 10). In the Betatron, a doughnut-shaped tron, In a transformer, winding or coil. Now if the current the flux lines increase, of the Betatron is similar transformer. the flux lines also change in strength. current a high energy circular Electrons much the same thing happens. vacuum chamber placed in a magnetic field. this magnetic field guides the electrons beam as the secondary coil. coil of a transformer Increasing flux to the “secondary” znd the circulating As for a Cyclo- path so that they move The windings of this electromagnet around and around inside the vacuum ring. can also act as the primary in a circular are injected into and the circulating the current electron to the magnet increases the electron beam is accelerated, gaining . energy. Of course, electrons were nothing else done, the circular path of the accelerating would spiral out and the beam would strike the walls of the vacuum chamber before much energy had been gamed. - 17 - In order for this not to happen, the strength of the magnetic field guiding the electrons increased Thus as the electrons as the flux is increased. enlarge their orbit, original radius. the magnetic field increases 7 the orbit to its SECONDARY COIL ALTERNATING CURRENT ALTERNATING ‘\ ‘\ \ \ . \ ‘\-;J,. .-;I 1 ‘\:,-’ ,/’ ‘x-4 / w CHANGING MAGNETIC FLUX \ i, i,,_ ,:;,” I’I ~ * i”:‘?; ‘;,; ,I / , ’ I ‘i I”‘1 - - MAGNET WHOSE COIL ACTS AS PRIMARY WINDING , I ! I CIRCULATING BEAM AS SECONDARY WINDING 493-10-A FIG. lo--The principle of the Betatron is similar to ordinary transformer action (a). The electromagnet which sets the curved trajectory of the electron beam also serves as the primary winding inducing energy in the secondary winding, the electron beam itself (b). - 18 - orbit is gain energy and try to and constrains PRIMARY COIL1 ALTSNG CURRENT in the circular The changing magnetic flux providing netic field guiding the electrons acceleration and the increasing can be produced by a properly The latter magnet or by separate magnets. mag- designed common technique provides more flexibility in design and operation. . These changing magnetic parameters a parameter which a Cyclotron tons can be accelerated flow. However, mean, of course, does not, “pulse rate.” continuously In a Cyclotron a Betatron must be recycled. electrons be restored, are extracted When the magnetic flux has in- from the machine, and the entire procedure A new group (‘cpulse”) of electrons over again. the pro- and can exit from the machine in a steady creased to produce the desired energy in the circulating celerated that the Betatron has electron beam, the ac- the original conditions must must be recommenced. is then injected and the cycle is started The new 340-MeV Betatron at the University of Illinois operates at a pulse rate of six pulses (cycles) per second. D. Reaching for Higher Energies With the Cyclotron, proton energies of up to about 20 MeV are achievable. During the late 1940’s, Betatrons were capable of producing 70 MeV. The aim for higher energies than these was made more practical the independent but simultaneous California : work of E. M. McMillan limiting resulted in two different of To “synchronize” ating alternating techniques for overcoming of achievable energies caused by the particles getting out of step with the alternating - at the University by and of V. I. Veksler of the U. S. S. R. Their studies of the Cyclotron method of acceleration relativistic electron energies to the circular voltages providing orbital beam traversals ating voltages can be slowed down as relativity in the beam the energy increases. . with the acceler- either of two things can be done. voltages, the Either the acceler- slows down the beam velocity, or - 19 - ‘1%ILlblFFw.- . . . ~_,_-- ~1111 *-.-‘.*,-y-,.r-nrr~,~ ____,. wb*. .~~EL.~CI”“.l^r?l.-~~- .._ -.-,-. .l-..___pl_l_----w4. .v.fi- --.---I s x”.,** rii*nri-.nr, 2 5~,i,‘~,mc4mx~uis’Y44~~*r n,.n-a. _ -.-- . . ..--m-1_-----. ..-. . . L -w..r Sh%, ,) -+‘***IRurl *cIwe+I. the guiding magnetic field can be increased in strength as the beam gains energy, thus constraining E. the beam from increasing Higher Energy Electrons: its orbit radius and time of motion. The Electron Synchrotron The latter of the above two plans was the first to be implemented. higher electron energies than practical was developed. Cyclotron The Electron Synchrotron method of acceleration voltage gaps in the circular The characteristic fact that electrons, velocity, is an accelerator Synchrotron which combines the energy increases due to traversals of path. of an electron which makes this technique practical being so light, constant velocity. the Electron with the technique of having the magnetic guide field strength increase as the electron alternating in a Betatron, To achieve Electrons is the are very easily gotten up to a near -maximum travel at 98% of the velocity of light, the maximum with only 2 MeV energy. The Electron Synchrotron into which electrons consists of a doughnut-shaped vacuum chamber . are injected at about this constant-velocity energy by a smaller such as one of the electrostatic accelerator their circular motion, passing through alternating vacuum chamber is surrounded follow the circular of the surrounding tron trajectory are traveling of the vacuum ring. ring magnet is synchronously increased. in one single circle of constant radius. constant velocity 11). - 20 - the field strength This keeps the elec- Because the electrons in a constant-length nating voltages at the gaps can continue to be reversed (Fig. begin voltage gaps in their path. The gain energy and become harder to turn, at essentially The electrons by a ring magnet whose field makes the electrons path defined by the interior As the electrons types. path, the alter-. at constant frequency I RF GENERATOR czNh 493-11-A BEAM FIG. 11--Principle of operation of a Synchrotron. The entire structure is doughnut shaped. Increasing the magnetic field in the guide magnet keeps the beam in a uniform circle. One or more voltage gaps provide periodic acceleration. The McMillan-Veksler several Electron built. Synchrotrons At Frascati, Synchrotrons larger work appeared in 1945. in the energy range of from 300 to 350 MeV were Italy and at the California are now operating ones, using some slightly Institute Higher Energy Protons: of Technology, Electron at energies well above 1000 MeV (1 GeV).‘(Even different principles, Section H below. ) Like the Betatron , synchrotrons F. By the end of that decade, have also been built. See must also be “pulsed. ” The Synchrocyclotron The other McMillan-Veksler alternative was used in the first attempts to . reach higher proton energies than achievable in Cyclotrons. Synchronization 1 Tinere are two common abbreviations for billion (tho7ssand million) electron volts. America uses “BeV,” Europe uses “GeV.” Because “BeV” means something else in Europe and because of the extensive international intercourse in this field, “GeV” is becoming more and more accepted world wide. “GeV” will be used here. - 21 - 76 I.- -- ..--- 2 -----” .._---. I_-(./ .-r-r..-.-*.w ---------_I-c_-,--n- _ LC .v u*r*r .c”-c m-%,---.-es --)L-w-c- .a----L.-r--..-- P-u - -‘T~*-*~.-.---u-..m-*-~^ of beam circulation with the alternating accelerating ducing the rate at which the alternating constant-strength voltage reverses This machine, slows down with increased energy. voltage is achieved by reas the particle the Synchrocyclotron, magnetic guide field so that the beam path remains from the center to the outer edges. As the spiral radius increases causes the particles the accelerating to drop behind the rate of alternation rf voltage is “frequency beam has a a spiral and relativity of accelerating modulated. ” This means that the rate of alternation of the voltage at the gaps is slowed down at the same rate the particle velocity increase is slowed down due to relativity the voltage changes only when the particles traveling effects. The polarity in the semi-circle dee can manage to get to the gap. The rate of voltage polarity quency of the rf generator ) is the lowest when the particles of the have reached their dees , ready for ec- This technique overcomes the problem caused by the relativity effect; in step with the cycling of the particles. The rf the changing dee voltage remains generator frequency decreases as the rate of increase in velocity becomes less. The first large Synchrocyclotron was operated at the University of California Rebuilt in 1946. This machine produced proton beams of energies to 350 MeV. later, of change (the fre- highest energies and are at the edge of the Synchrocyclotron traction. * voltage, In Switzerland this machine now achieves energies to 740 MeV. Russia there are Synchrocyclotrons and in capable of energies to 600 and 680 MeV, respectively. Were Synchrocyclotrons this, to be built to achieve energies much greater a problem arises in retaining Even with this problem of view of economics. Synchrocyclotron the particles Synchrocyclotrons at the University limit are huge machines. of California . stably in their outer orbits. there is also a practical overcome, than from the point For example, the uses a magnet which is over - 22 - ‘-.--.. ‘c-.” .-., Im#-_nc “a. >*- v--‘T’-‘J”RIIc. -.... “/.,‘._I.~~~,q.j/ aies-r.rrt.*S*aw‘e.sr-.l’ --- - .w,H. .* ia. . . ‘1 hwl”.i--.. -*cl)-* .;,:z----; ” I , ___ -__^_ *.-*+.---m.-/_,, _ .,,- “i ^, ,.._ _.. I. I -,.~“,.*^-v.---)l l-97-^- 15 feet across and which weighs over 4000 tons. larger than this is extremely becomes higher and higher To build a Synchrocyclotron The cost per MeV of energy increase expensive. as the magnet becomes larger and larger. G. The Proton Synchrotron To reach higher proton energies, McMillan-Veksler Synchrotron, it was decided to return to the other This was the technique used for the Electron alternative. the technique in which the strength of the guiding magnetic field was increased as particle The resulting energy was increased during acceleration. like the electron Proton Synchrotron, shaped vacuum chamber into which the beam particles net surrounding machine, has a doughnutA ring mag- are injected. the vacuum chamber keeps the beam moving circularly As the particles center of the chamber. along the gain energy from traversing the alternating voltage gaps, the strength of the guiding magnetic field is increased. the particles continue to travel . in a common single circular ^ Thus path of constant radius. There is a major difference, As mentioned above, it is easy to get electrons chrotrons. of light, trons between Proton and Electron however, where their velocity in a Synchrotron remains nearly constant. complete each circle Syn- to near the velocity This means that elec- in the same amount of time regardless of energy increase. This is not the case for protons. v They do not achieve this convenient near- constant velocity until they reach energies they do continue to increase in veloc&ty. as protons gain energy in a Synchrotron, . Because the path the protons travel is a constant the alternating rf generator Therefore, of about 5 GeV or more. voltage at the accelerating gaps. must be frequency modulated. one, they continually gain on So once again, the alternating In the Synchrocyclotron, the rate - 23 - - ( .-m. -,“^*(-.< ziT.+&nn*r ________ ra.wrrrt**m+uww --.-- _____-cl-rrfi”~~*“-wl)ri-y- _-pm_llm.-C. .w.rw.x*r---.--.Fw-4 *-----...-L-“.--m I_” .,,-. “.. ,T. ,*\,11. *.sq .w.*- Jv cx-r*r.awemr. ‘~~‘ym. of voltage alternation ton Synchrotron, be increased is decreased as higher energies are achieved. In the Pro- the opposite is the case: The frequency of the rf generator as the particles speed up with increased must energy. Because there is no spiral motion in a Synchrotron , the guide magnet need not cover the entire area of the round machine. Instead the magnet is constructed just around the ring-like This cost saving is the big factor vacuum chamber. making the Proton Synchrotrons preferable to Synchrocyclotrons The first two large Proton Synchrotrons, completed in the early 1950% , were the Cosmotron at Brookhaven National Laboratory the University of California (6.2 GeV). at high energies. Similar (3 GeV) and the Bevatron at to these are several more, including ones in Russia (10 GeV), in France (3 GeV), at Princeton University (3 GeV), in England (8 GeV), and at Argonne National Laboratory (12.5 GeV). High energy Synchrotrons require that the electrons or protons be injected into the accelerator after being previously accelerated to an appreciable energy. ^ This is usually done by employing a smaller accelerator such as a linear accelerator, itself fed by an electrostatic pulses of particles introduced injector. These injectors assure that the into the Synchrotron have sufficient energy to enter the designed orbit. H. Raising the Limits: A new principle The Development of Alternating of guide magnet design, which was started in 1952, has led to a series of accelerators cally practical Gradient Accelerators capable of much higher energies with any of the above techniques. than were economi- The accelerators described above all focus their beams using a technique called “weak focusing. ” To keep the circulating or radially, beam from being displaced from the desired orbit, during acceleration, either axially the instantaneous guiding magnetic field is made to be a little less toward the outside of the circular - 24 - machine than it is at , the same time at smaller radii. This slight distortion ( a “gradientl’ field ) pro . vides restoring forces to maintain the desired orbit. ’ However, magnet design problems the solution to made weak focusing more and more expensive as higher energies were reached for. The innovation which replaced weak focusing at higher energies is called “strong . focusing” or “alternating gradient focusing. ” The technique developed Alternating was to divide the guide magnet into sections around the machine. sections would have a slightly larger ius while the intermediate netic field at larger comprise instantaneous magnet field at larger sections would have a slightly radius. rad- less instantaneous mag- Together these alternating gradient fields would a converging lens system which would provide the necessary focusing more practically at higher energies. This technique has been applied to many kinds of accelerators. gradient Electron Synchrotrons, using this focusing method, have been built for beam energies to 6 GeV at Cambridge, and at Erevan, Alternating Alternating Massachusetts; at Hamburg, Germany; Russia. gradient National Laboratory, Proton Synchrotrons are in operation at Brookhaven New York ( 33 GeV) and at Geneva, Switzerland ( 28 GeV). The Being put into operation is a machine in Russia to achieve up to 70 GeV. U. S. Atomic Energy Commission nating gradient Proton Synchrotron is supporting the establishment of an alter- to reach energies as high as 200 GeV. - Scientists at various laboratories 1 The 12.5 “zero -gradient shaping of the field decrease are making conceptual studies of even larger GeV Proton Synchrotron at Argonne National Laboratory, the synchrotron ” or ZGS, accomplishes its weak focusing by special edge faces of the guide magnet rather than by having the magnetic at larger radii. - 25 - .I -.., _... “. -_I . ../ . .----v.F.w.n...e.--. .T( _. . jl _ ” .I *.#.avserwII1 nTIC”. ‘.e.ll*dYJZF alternating gradient Synchrotrons, perhaps several miles in circumference, to produce proton beams of many hundreds of GeV. Even the early-appearing Cyclotron has been embellished Using an “azimuthally of this technique. looks like a pinwheel of alternating ing , AVF Cyclotrons by a modification varying magnetic field” (the magnet high and low field areas ) to provide focus- are in use today providing beams of several hundred MeV I of energy. I. The Future Nothing but economics limits Synchrotron. New innovations the size of an alternating gradient in beam handling and in adapting such machines to higher and higher energies are constantly being developed. acceleration Proton Thus this kind of of protons can continue to higher energies with no theoretical However, this is not the case for the acceleration particle constrained radiates energy away from itself because of this acceleration. as the particles to move in acircular of electrons. orbit by a central limit. Any charged accelerating force This means that in the beam are given energy to produce acceleration, they must also be given additional energy to compensate for the energy lost because of this “synchrotron *’ radiation. The higher the energy the particle the greater has been given (the higher its velocity ), is this energy loss by radiation. For any type of particle, omenon does not become a nuisance until the particles the velocity of light ( “relativistic velocities” are traveling this phenat nearly ). . The amount of this energy loss at a given energy is much greater for the smaller electrons than for the much more massive protons. For protons, the energy loss is not so large that it cannot continue to be made up “for by increas ing the energy added at each accelerating gap. For electrons, however, the - 26 - pr -.’ -:; x ^-~.a.wN.~.~,.+onn*zc --..- _.-“--F- -y-___y-r.,-lw$~-*r~~+io vw$wc -*x.ur,.,.c.. _xI. __... *:*a. . ..-. “. -.., .__^..-e . -..--.w. .~ -.. “_1” __I-.~ * * “.bl”m *- .myc.*w -v energy loss is so great that before reaching an energy of about 10 GeV, the electrons in an Electron Synchrotron begin to lose more energy than practical power supplies can replace. ’ Therefore, efforts to provide electron beams of energies higher than prac - . tical in Electron Synchrotrons had to be confined to extending the development (and size ) of linear accelerators . this relativistic where the absence of circular motion removed obstacle. ^ . 1 The energy loss per unit time or per turn due to synchrotron radiation in a constant-radius Synchrotron is proportional to the fourth power of the par title’s total given energy and thus is a function of the fourth power of its velocity. Conversely (and fortunately) this energy loss is inversely proportional to the fourth power of the particle’s rest mass. - 27 - . ,. ._“__ ,..w-e --_.- -----.-,“.x,~-x-eF-TD ..,_ ----. w--m+- --,__.-- _~ -.-. ~“WmrrVprWrYCYcCu -.. .X--..--l-~--.l-_I.^~““. _ .w~- --.._ -.- ,.,,” .-^-.-.jl ,. .-ll-_ll_r-__l”_-l....-*-6.--*p V. Ln the previous ignored. section, LINEAR ACCELERATORS the development of linear This was done for two reasons: (1) Linear accelerators accelerators in a class by themselves and were developed in parallel the circular which received much more widespread accelerators cause the subject of this writing In the description of electrostatic accelerators generators, mention was made of the con- gaps in succession in a line. In the earliest and simplest free passage. connected together electrically. Alternate For instance, several voltage form of the linear ac- Holes are bored in these plates a series of plates is placed in a line. the beam particles attention. (2) Be- is in order. by allowing a beam to traverse to permit from a more detailed exposi- cept of achieving acceleration celerator, are somewhat with but separately is a linear accelerator, tion of the techniques involved in linear was virtually plates (electrodes) all odd-numbered are electrodes are connected together and tied to one terminal of a radio frequency generator. All . ^ the even-numbered electrodes are connected together and tied to the other terminal of the rf generator. Thus during one-half cycle of the rf generator, the electrodes and half are negative. are positive If beam particles are placed between every other pair of electrodes, half they are are in a proper voltage gap and are accelerated. As soon as they pass through the hole in the second electrode, cycles and the polarities electrodes are reversed. the rf generator The particles are now between the electrodes on the of the . other set of every other pair of electrodes. versed, this second set now provides continues as the beam particles But because the polarities acceleration. traverse is recycling or recycling r gap after gap and gain energy step by step. Of course this energy gain means the particles Because the rf generator This alternation are re- are also gaining in velocity. at a constant frequency, - 28 - the electrodes have to be spaced farther and farther The particles apart down the accelerator. are moving faster and must not pass through an electrode before the rf generator has had time to recycle. To take advantage of the most efficient the electrodes cylinders, are in reality part of the output of the rf generator, While the particles cylinders. are traversing they see no voltage field and are not accelerated. therefore are often referred to as “drift longer drift tubes is determined and cross the (These electrodes tubes. “) The length of the successively so that when the particles leave one drift tube a small gap to the next drift tube, the voltage from the rf generator is just such to provide the most efficient The first energy gain. beam achieved in an accelerator of this type was in one built about 1928 in Germany by R. Wider’de based upon a 1925 concept of G. Ising. drift tubes were housed in a large glass cylinder. The metal Heavy positive particles were injected at one end and passed through the successive drift tubes and gaps. This successful (Fig. 12). machine was the direct-ancestor of linear or “resonance” accelerators EVACUATED GLASS CYLINDER y I PARTICLE SOURCE I RF GENERATOR I I I 493-12-A FIG. 12--Simplified diagram of the Wider’de Qype of linear accelPositive beam particles will be accelerated erator. in gaps 1, 3 and 5. When the rf generator recycles, the voltages on the drift tubes reverse so that acceleration takes place now in gaps 2 and 4. - 29 - - -e.- Wm. ..-.4..Q.**y- .,T.--“V z,+. _” . .. -----.---..-YI_I . -.:v*-- -.--.._-_.---- -., ..I w-s-em --.“.“...“w -..*.. I .-.*.-* ..-.____ _ - - _ .,. . .._ “,-_,c ..--.- -. -,-. During the 1930’s, machines of this type were built and successfully ated with as many as thirty linear accelerators, drift tubes in the accelerator however, were limited cause of this, to accelerating as their energy increases. protons and electrons, These only nuclei of rela- The lighter reach very high velocities either ridiculously glass cylinder. This was because only heavy ions remain at tively heavy atoms (“heavy ions”). low enough velocity oper- particles, at relatively such as low energies. long drift tubes would have been required order to permit such light particles slowly recycles or else it would have been necessary to use rf generators recycle at extremely rapid rates, in to continue to move while the rf generator on the order of hundreds of millions every second. Long drift tubes were not practical of sufficient Be- which of times and high frequency generators power did not exist at that time. During the late 1930’s, working on the development of high frequency radar system components, the British developed a high frequency oscillator, wave tube called the “magnetron. ” Wartime radar research in other types of high frequency oscillators. of high frequency power made possible further light particle beams. This post-World at two institutions. at the University of California under the direction linear accelerator. resulted The appearance of these sources work on linear accelerators War II work was concentrated Work on proton linear accelerators for primarily was empha- was performed at Berkeley. Shortly after World War II, a team at the University Laboratory in America The development of electron linear accelerators sized at Stanford University. a micro- of L. Alvarez1 of California Radiation developed a 32 -MeV proton This machine used a slightly different principle than that of ‘An important member of the Alvarez team was W. K. H. Panofsky, Director of the Stanford Linear Accelerator Center. - 30 - now the . the heavy ion linear accelerators described above. Rather than housing electrically connected drift tubes in a glass cyliner, Alvarez followed a concept of High J. Woodyard and housed isolated drift tubes in a large copper cylinder. frequency power was coupled into this cylinder ,. 1 . The large copper cylinder rf generator. ?esonant by a small loop from a microwave was thus “excited” and acted as a cavity. ” The dimensions 39 inches in diameter of the copper cylinder, and 40 feet long, were selected so that when rf energy is coupled into it, a high voltage field is set up between the two ends of the copper cylinder. ant microwave i t ! : 1 field reversed 200 million In this machine this reson- times per second. This resonant electric field sets up standing radio waves in the cylinder. field in the cylinder induces alternating end of each half-cycle, current The alternating magnetic flow on the drift tubes. At the each drift tube is charged oppositely at each end (no net charge on any tube), and all drift tubes are charged in the same way. With each half-cycle, -this charge orientation reverses. Protons are injected when the input drift tube is positive and the closest end of the next drift tube across the gap is negative. The protons cross this gap and are accelerated. ator reverses, the protons travel along this next drift tube. By the time the protons reach the far end of this drift tube the rf generator electric field in the cylinder positive charge. (nearer) is reversed, has again reversed, Once again the protons traverse field is in the accelerating a gap toward the negative phase (half-cycle) a gap. During every other half-cycle, drift tube charge distribution is reversed, the and the far end of the drift tube has a end of the next succeeding drift tube, again achieving energy. as the electric crossing While the rf gener- So long the protons are when the field is reversed, and the field is ““decelerating, . the l1 the protons are in a drift tube. Each succeeding drift tube is of course longer than the preceding one because the protons are then traveling - 31 - at a higher velocity. EVACUATED METAL CYLINDER --, i ELECTRIC FIELD FILLING CYLINDER .. i PROTON ;OURCE Is , ~- _ -I RF GENERATOR I 493-13-A FIG. 13--Simplified diagram of the Alvarez type of linear accelerator. Protons in the gaps are accelerated. When the..rf generator reverses the field so that the charge distribution on the drift tubes is reversed, the protons “hide” in the drift tubes through which they are moving. On the next field reversal, the polarities are again as shown the protons have reached the next gaps, and further acceleration takes place. In this 40-foot-long The protons cylinder there are 46 drift are injected at 4 MeV with a Van de Graaff machine, ator is actually nine vacuum-tube cylinder and each providing self-excited 250 kilowatts oscillators, operating The rf gener - each coupled into the requires this accelerator in order to keep the average power output of the oscillators range. Thus the oscillators length. of power. The high power output of these oscillators “pulsed” tubes of increasing to be within their are on for less than a thousandth of a second 15 times each second. This historic machine was dismantled Southern California, At the University celerator and put back into operation of Minnesota, which provides 70-MeV protons. ‘-- .- * IUZ p+-m&vrwEw-v: -w....-“r. - of l there. J. H. Williams - ------XL‘. in 1958, moved to the University has built a proton linear ac- This machine is built in three sections, 32 - _ V.-P w.evm rrireb*rrr __. 7.2 - - __ _ . -..1 _ . . _._ ----..rl _,.- ~... _.. .cew.-.* CC--d-w. *. each much like the University generator of California especially called a “resnatron” The British machine, and each powered by an rf developed just for this accelerator. Atomic Energy Research Establishment has a proton linear accelerator at Harwell , designed for even higher energies. Proton linear circular accelerators The injectors proton machines, California are also used extensively The injectors at Moscow are lo-MeV for the Alternating Brookhaven and at CERN are 50-MeV This kind of accelerator for large for the Bevatron at the University and for the Synchrophasatron accelerators. as injectors of proton linear Gradient Proton Synchrotrons proton linear at accelerators. is eclipsed by the capabilities of proton synchrotrons and so probably will not be much extended for the purpose of achieving high energy protons. mind. However, developments For instance, in this area have diverged with related aims in by not requiring high energies the rf generators can be on for longer periods of time and thus proton beams of very high current per second ) can be produced. High-current beams have particularly (protons useful applications in nuclear research. Again, developments have continued in the field of heavy ion linear ators to achieve higher energies for such particles. able to elementary particle physics, physics and nuclear chemistry. duced in cyclotrons accelerator acceler- Although not directly applic- such machines find great use in nuclear Energies and intensities are too low for these experiments. of heavy ion beams proThe heavy ion linear is ideal for this application. Meanwhile, back at the Farm, ators was preceding and proceeding the development of electron linear acceler- . along with the above development of proton linear accelerators. - 33 - VI. DEVELOPMENTOFTHEELECTRONLINEARACCELERATOR Two things took place at Stanford during the 1930’s which made possible the University’s later specialization linear accelerators. One was the development of practical electron acceleration. fier, the “klystron” and success in the field of high energy electron resonant cavities for The other was the invention of the high frequency amplitube. For a while in 1934, Stanford Physics Professor graduate student Russell Varian roomed together. ing a way of producing high energy x-rays William W. Hansen and Hansen was interested by electron bombardment in find- of a target, without involving the expense of building a huge electrostatic electron Hansen and Varian discussed several techniques, each because of impracticality A. discarding or cost. The Resonant Cavity Principle: The “Rhumbatron” Hansen conceived of the idea of passing electrons which oscillated accelerator. through a high voltage at such a high frequency that there would be no time for high voltage breakdown and a large vacuum chamber would not be required. was to couple some high frequency power into a small, copper cavity about the size of a small box or can in such a way that the cavity would oscillate. one end would be positive and the other negative, His idea First then the situation would reverse. Small holes were bored in the center of each end of the cavity so that electrons could pass through. If the electrons tive and the far end positive, enter the cavity just as the near end is nega- the electrons are accelerated through the cavity, leaving the far end with higher energy than that with which they entered. device became known as the “rhumbatron. ” (Fig. This 14). The power feeding the cavity came from a high frequency rf generator was coupled into the resonant cavity with a small coupling wire. and In 1936 and - 34 - y ..,. ~-~~wLvpme,*-~s”“” r i -” I..-” If-“- “FJ -*C-v- _ :“‘“‘“-““.~-“~~~~T~~‘~~.-~ _.... - zz-z-2: ‘-rYn-T:--T:L -p-.I-..-,-.._““,- “.~~--” 7,” INPUT POWER PATH OF ---mmELECTRONS 493-14-A FIG. 14 -- Single resonant cavity accelerator using the Rhumbatron principle. The input power is a high frequency oscillating radio (microwave) signal which reverses polarity many millions of times per second. In the diagram, the half cycle of the field, when it is in the accelerating phase, is shown. .. 1937, Hansen built several different rhumbatrons of different sizes and &apes, striving to obtain the most efficient resonant cavity. The natural extension to such a device is of course to place several resonant cavities in a long line, end-to-end (Fig. 15). Each successive cavity would then add more and more energy to the moving beam of electrons. be impractical ator. However, to try to “excite” each resonant cavity with an individual It would be much simpler to connect together electrically it would rf gener- each of the power . input coupling wires and to feed them with the output of a common rf generator. j Of course, 4 the excitation of each cavity must be properly age reversals (oscillations) take place properly timed so that the volt- as the electrons leave one cavity and enter the next. To do this, the signal from the rf generator would start at the same end of the device as the electrons would, and travel down the line - 35 - ‘~ - --.- ----- -__------.- m-w--me.-- ------> .----.--- -I - connecting the coupling wires at the same speed the electrons through the center of the in-line would travel resonant cavities. PATH OFF ------a-----w-----m------------ --a POWER 493-15-A FIG. 15--Multiple resonant cavity accelerator. In this scheme each cavity is excited with input power in succession from a single source, using individual couplers. B. The Traveling Wave Concept Such a complex distribution design and donstruction relationships of a multiple between cavities to another technique, scheme is possible and has been used. But the feed system to achieve the desired timing is difficult the utilization in execution. of a traveling Into one end of his string of resonant Instead, radio wave. cavities, Hansen decided to introduce a radio wave which would travel down the length of the device. successive crests alternating between negative and positive. could be caused to flow down the cylinder Hansen resorted A radio wave has If such a radio wave (made up of the cavity string) the pos- tive wave crests and negative wave crests in motion would create a moving electric field delivering into the cylinder, energy to each cavity. * Electrons coicident with the appropriate could than be introduced 1 wave crests. ‘The essential principles of the design of a traveling wave linear accelerator were established independently and nearly simultaneously at Stanford and at the Telecommunications Research Establishment at Malvern, England. - 36 - -_...-__.--.-. -e-v-- --..- -.^-pI<~MW#%TR.*T.-.---.?+ .-_--.-w--. r... eu- -.- -_ .--.-w 7-i -a.- Hansen wrote, “Now if a particle be introduced onto the leftmost with a velocity equal to that of the wave, the particle the right and will, velocity therefore, is controllable; is accelerated, be accelerated. wave crest will feel a steady force to We have assumed that the wave let it be adjusted in such a manner that as the particle the wave is also, and at just the same rate, so that the particle will always ride the crest of the wave and will always feel an accelerating The particle will then gain energy at the expense of the field, and, if all the above can be made to happen as assumed and the numbers are favorable, a practical means of accelerating charged particles. To draw an analogy: Just as a surf-board rider force. we may have lfl is accelerated by riding the crests of ocean waves, Hansen believed electrons onto the beach could be accelerated through a string of resonant cavities by riding the crests of radio waves (see Figs. 16 and 17). C . The First Prior Stanford Machine: The Mark I to World War II, Hansen was never able to put together a working model of such an accelerator with the high energies of interest to the physicist. One of the things which held back the effort was the lack of a suitable high frequency, high power source of the traveling radio wave. During the war, the demands of radar resulted kinds of such microwave power tubes. was a high power microwave . t - oscillator in the development of several One of these, developed by the British, tube called the “magnetron. ” The magnetron saw extensive use in the war effort as a power tube for radar sets. After the war, Hansen together with Professors Woodyard examined former linear accelerators. 1 conclusions regarding E. L. Ginzton and J. R. the feasibility This group, among several others, Ginzton, Hansen, and Kennedy, Rev. Sci. Instr. - 37 - of electron recognized that the 19, 89 (1948). . + (b) + (4 493-16-A FIG. 16--Simplified presentation of the traveling wave principle. A high frequency radio wave is caused to flow down an electrical waveguide (a). Negatively charged electrons are pushed by the negative wavecrests and pulled by the positive wavecrests to cause motion to the right (b). This is not unlike the horizontal acceleration of a surf-board rider on ocean beach waves. . i 493-17-A FIG. Ill--Cutaway drawing showing internal configuration of accelerating waveguide showing three cavity-forming disks. The dimensioning and spacin, e of these disks control the velocity of the riding” electrons can traveling wave so that the “surf-board remain in step with the wave crests. - 38 - - -- .--. .-. -9.b “Mmn-Dln.. _ _-._,,. _. -.*. - . ..-- r--.-I_- -.-.-y.:. _-_--v-L_----I ___ c__ .-.,-.. “. -.-. . - war-developed magnetron in the range of several made it practical MeV with available to build electron linear magnetrons. that any higher magnitude of energies would require accelerators (It was also apparent further development of power sources in order to obtain a total power of several hundred megawatts. ) In 1947, the first machine, Stanford traveling wave electron linear accelerator later known as the Mark I, was 3-l/2 feet long (see Fig. 18). It contained 38 cavities megawatt magnetron oscillator Mark I generated a 1.5-MeV carried was operated. inches in diameter in its length. out under the sponsorship beam. Development and three Using a 0.9- for the source of the traveling electron This radio wave, the of the Mark I was of the U. S. Office of Research and Inventions, later the Office of Naval Research (ONR). For a Cuarterly Status Report on the FIG. 18-- The original Mark I electron linear accelerator photographed . in the Stanford quadrangle and being held by, left-to-right, S. Kaisel, C. Carlson, W. Kennedy, and W. Hansen. - - 39 / , ,?I -.----.‘-*-I.. . - . ..,~~,~.,..-Il~~~vYse‘.-lr. -.-- --1 I.,w-.rr”,*, ..-aw.~‘~~~.-.Be.~~“.-,T.vI V-m-*%,- r.,. .- cd 379y . . -.-.--r.cr-.-~WrP.--r*. ’ ’ 7t __ 9% Hansen submitted a one-sentence report : “We have accel- at this time, project erated electrons. ” Eventually the Mark I was extended to a total of 14 feet and 1 provided 6-MeV electrons. To build an even higher energy accelerator, sources would be required Hansen recognized that rf of power higher even than available with magnetrons . To achieve such a device, Hansen decided to turn to the development of a high power amplifier to increase the power available from existing rf oscillators. This led him back to the second, parallel of the klystron D. Stanford story: tube. The Klystron Tube. Radio detection and ranging (“radar”) is based on the transmission them to be as small as possible. signals to have as short a wavelength the transmitted and re- The ability to move and point the anten- ception of high frequency radio signals. nas requires the development This in turn requires the radio (high a frequency ) as possible. In addition, radio signals must be of very high average power so that reflected signals can be received from distant objects. The approach of World War II accelerated cillating and amplifying research and development of os- radio tubes to provide these high frequency radio transmissions. The British magnetron, results of this work. But similar activity was being carried Russell Varian’s brother nautics Administration reflection mentioned above, was one of the Sigurd was an airline In 1936, the brothers weather navigation. for determining (microwave) pilot, out at Stanford. concerned with bad sent a suggestion to the Civil Aero:- the height of cloud layers by timing the of light signals aimed at the clouds. - This led them to consider using 1 The Mark I beam had a pulse width of 0.8 microseconds, a repetition rate of 60 pulses per second, a peak current of one milliampere and an average current of 0.05 microamperes. - 40 - ‘-- ---“I . ..- --~l,.~.x.-.l-“.” ,---_ . III_y_---u_xI_yL”_,l_..~ .,. --1 ” _,C...l. .eex--- L __- .,..eF -w- _e----..--11* __“._-^“- . .L,V.X,I ..__..-. -w--rrrw.lr.r9- -..r * .*y.*.* ~.Ywrm”ur*~*r-‘~~~~*~‘ microwave reflected radio signals, which would penetrate clouds but which would be by solid objects (see Fig. 19). . TRANSMITTED HIGH POWER RADIO WAVE ~ ,\,,i;l.-,~~~~\i~~~~ \ ‘\’ RADAR TRANS-CEIVER \’ \ \’ \ \’ - .. TRANSMITTED PULSES OF ! HIGH FREQUENCY RADIO WAVES REFLECTED PULSES OF i WAVES W FIG 1 19--Principles of radar operation. High power microwaves are transmitted toward an object. Some of this is reflected from the object and returned to the radar set. Analysis of the two waves provides information about the position of the object. High power transmission is required so that the small part of the small reflected wave can be detected. Early designs used continuous waves (a). Later developments permitted pulsed transmission (b) . By early 1937, the Varian brothers * 493-19-A Stanford working with Professor crowave devices. were both research Hansen both on the rhumbatron Russell Varian dedicated himself technique for amplifying associates at microwave I and other mi- to trying to conceive of a signals to powers useful in radar-type - 41 - .-_. - .’ ‘--T- -“..--_-.w-e,- w-r- . .--“. - --. -.ms.-...m.-~-.L..., . _..-_ .____” - --- -.._ “__ _.*--I_w . .“I_-. ” I- ” -_**. ---- . --.-. - “.. ^ ---..---... ..“. _ -.*a ^rr,....-*r*-n-w. .--. “._” ” applications. After the team having designed and built several kinds of devices, on June 5, 1937,Russell The klystron is a microwave and Russell Varian’s rhumbatron Varian conceived of the klystron principle of velocity on his recognition cavity, Varian’s As described above, the energy from an rf generator velocity modulation principle electrons, was based leaving the rhum- would not be in a steady stream but would appear in “bunches. ” resonant cavity, the velocity electric is introduced in the accelerating Electrons into one side of an oscillating of each electron will be affected by the status of the field in the cavity. field is maximum velocity. modulation. of the fact that the accelerated If a steady stream of electrons oscillating tube based on Hansen’s rhumbatron was a resonant cavity which transferred to electrons passing through. batron amplifying principle. arriving Electrons arriving just as the electric phase will receive the greatest increase in a little before or after this time will be speeded up a little less. Those electrons appearing at other times will be slowed down. .. Now if all these electrons are allowed to pass down a drift tube after they leave the cavity, the faster ones will begin to catch up with the slower ones so that eventually bunches of electrons are formed. Varian’s idea was to use these bunched electrons to excite another resonant cavity in reverse. cavity, a small microwave oscillations In the first radio signal caused the cavity to oscillate affected the velocity of a traversing electron beam. Varian placed a second cavity in the path of the bunched electrons. The bunched electrons ing through the second cavity caused this cavity to go into oscillation microwave t signal did the first The oscillating cavity. *‘excited” second cavity then induced a current cavity to couple out the microwave and these pass- just as the magnetic field in the . in a small coupling loop inside the signal generated by the bunched electron beam (Fig. 20). - 42 - ., ~~~-w~~~~q4%q~~*“*‘-.“.-“., ” .--.-. I’ .-^_ .CI 1 L ,“_ .I*+... ,.. _LI.%.sIW ‘* -e-e-e._*.:_uI” ---I-^----.---‘-- ._..__ _- ,.... h - . x -‘-.‘,y,- .-...-- , , _,_-- I ,, ..-, v--m ,, “_ .) _-..,“___,, __ -.-vl.--” AMPLIFIED HIGH POWER MICROWAVES LOW LEVEL MICROWAVES TO BE AMPLIFIED DRIFT STREAM FIRST CAVITY ( BUNCHER TUBE ELECTRON BEAM COLLECTOR SECOND CAVITY ( CATCHER ) ) 493-20-p. FIG. ZO-- Principle of klystron amplification. Low level microwaves excite the first cavity to oscillate. The electron stream enters from the left and is bunched by the oscillations. The bunches in turn excite the second cavity to oscillate. The oscillating energy in the second cavity is taken off as amplified microwaves. The microwave same frequency radio energy coupled out of the second cavity will have the as the microwave radio signal driving the second cavity has been excited by electrons ever, the microwave the first cavity because bunched by the first cavity. How- signal coupled out of the second cavity will be of much higher power than the microwave signal coupled into the first cavity. This is because the power given to the second cavity comes from the bunched electrons I themselves - which can be given high power before injection Thus amplification i plified first , being given increased cavity in the klystron the “catcher. I. has taken place. A microwave into the first cavity.. radio signal has been am- power at the expense of the electron stream. The is called the “buncher , ” the second cavity is called ” - 43 - : ---. ._ _____ I,- --I. ---n-T. .w~r-;***P-j>,-~~p‘- ..__.___ -u ..-. _ ._._ , ._ _.____.--.. -..---. ---.-x-I--_I.-___c-_-,-___ - -.--. Jn August 1937, the first such klystron ated by the Varian brothers was constructed and operat Stanford. For the next two years, their klystron amplifier the Varians and Hansen concentrated in order to achieve better amplification on improving and higher power. These early tubes provided a continuous output signal useful in early types of special purpose radar systems. However, in England the concept of pulsed radar was becoming well advanced. This kind of radar uses only short bursts of microwave power spaced out in time. Measuring the time between transmission and recep- tion of pulses was a more feasible technique for obtaining range information. In the early 1940’s the British were able to develop klystrons, based on the early work of Hansen and the Varians , capable of producing up to 20 kilowatts of pulsed microwave In the meantime, development, power. the British and by late 1940 and early 1941 they had achieved considerably greater power than the klystron’s watts. Because of this earlier the further had also been actively working on magnetron 20 kilowatts --perhaps success, the British development of the magnetron, as much as 150 kilo- put all their emphasis on and did not continue any additional development work on the pulsed klystron. In 1944, Ginzton went to England and investigated klystrons. After his later return to Stanford, to demonstrate limitations, istics the feasibility for klystrons ator then being investigated i of the generation Although the principal of high pulsed aim of their study was of very high powers and to determine the specific work was directed required work on pulsed Ginzton together with Professor M. Chodorow began a study of the possibilities power by means of the klystron. the British ultimate towards trying to achieve character- to drive a very high energy linear electron by Hansen. - 44 - acceler- . So two parallel tron linear endeavors were begun at Stanford. accelerator develop klystrons to develop energies in the BeV range. The other was to capable of producing the high power traveling to power such an accelerator. Office of Naval Research, of a billion-volt One was to design an elec- In 1948, Stanford submitted presenting in considerable waves necessary a proposal to the U. S. detail arguments in favor Under sponsorship electron linear accelerator. the project was started in 1948. This ONR-sponsored research of ONR, work on and development was known as “Task 16.” Extensive work was also started on the development of the high power pulsed klystron. March This part of the ONR-sponsored 1949, the first tube operated the vicinity E. such high power klystron at a frequency The Next Machine: a power output in The Mark II to house a l-BeV were underway, of the high power klystron Stanford began to con- electron linear accelerator. design work was begun on the 1 -BeV machine, prototype This of 20 megawatts. struct a building’ were intensified, research and construction With ONR supand development was begun on a machine. This last machine, meant to provide an intermediate ward the eventual construction of the l-BeV one of the many sections of the larger . tube operated successfully. of 3000 megacycles and delivered Beginning in 1948, several‘ projects port, activity was known as “Task 23. ” In milepost on the way to- machine and to act as a prototype accelerator, was known as the “Mark of II. ” ‘This building was called the Microwave Laboratory, a research facility in Stanford’s Graduate Division, with Professor Hansen of the Physics Department as Director. When Professor Hansen died in 1949, Professor Ginzton became Director. Four years later another building was built to become the Microwave Laboratory. The original building housing the accelerator became the High Energy Physics Laboratory. - 45 - Built under the direction of R. F. Post, the Mark II was first ated in October 1949, using the first high power klystron microwave eter, klystron was built in seven two-foot-long oper- tube built under this program. provides the accelerating traveling The wave by amplifying The Mark II, signal provided by a magnetron. successfully 3-l/2 a inches in diam- subsections for a total of 14 feet. Each of the seven subsections contained 23 cavities. Operating at 2855 megacycles, electron energies of up to nearly 40 MeV were obtained with peak beam currents of about 10 milliamperes repetition in one-microsecond pulses at 60-pulse-per-second rate. The Mark II, sometimes modified and rebuilt, has been in use for experimentation in electron physics since 1950. F. The Mark III The contract between the Office of Naval Research and Stanford University, for work leading to a billion-volt calling effect in June 1948. An organization up to carry out the work. named the Microwave The Laboratory Stanford’s main quadrangle, accelerator electron linear accelerator, went into Laboratory was set work began in the “physics corner” of but in early 1949, the building to house the large was completed and the work of the Laboratory was transferred to the new building. During the early years of the contract, areas. The theory of microwave work was carried electron linear accelerators advanced. Investigation was carried determine which were most suitable for electron acceleration. for transmission of traveling was studied and out of various accelerator rangement of resonant cavities forming perly called “waveguide, ” referring out in several the accelerator structures (The linear ar- structure to the fact that the structure radio waves. ) Microwave to is more prois designed measuring techniques - 46 - _ .+“l-j.Ml 1_.*- .e”a.ee.u- - ^L____,___, ~.-~--~ “. ._... ~_._ “___-.l-_---i-..-r-*” -,*, * %.w~w,%~~-~,>**.‘~* _yI_.--.SW r’ -_l_l__C_ cI1 -,a.*s..4- J I .*I ~*ru;r.*~,~~,~-’ - were developed for testing accelerator accelerator principle accelerator. amplifier was carried on and off were developed. and construction Mark I 6-MeV of the high-power Components for the large accelerator Mark II accelerator klystron were designed was operated with the new components, including the new high power klystron. accelerator, now known as the Mark III, was begun. subsections, into the The modulating devices for pulsing the klystrons The prototype The accelerating research in order to be able to provide the necessary traveling waves for the large accelerator. and fabricated. Further out on the magnetron-powered Design, development, were intensified components. Construction waveguide for the Mark III was constructed each containing 22 cavities nular disks and four-inch-diameter of the large in two-foot-long assembled with extreme care from an- tubing of selenium-copper. sections were then clamped together to form the ten-foot-long Five such subaccelerating waveguide sections . Each ten-foot amplifier, all the klystron section in the machine was to be fed by one klystron amplifiers to be driven by a common magnetron oscillator. The Mark III first operated on the night of November 30, 1950. At that time, a length of 30 feet of accelerator With each klystron providing this operation delivered In the following inch-diameter was assembled, an average of eight megawatts of microwave power, an electron beam of about 75 MeV. months, the accelerator accelerator supplied by three klystrons. grew in ten-foot was mounted on 20-foot-long steps. The four- I-beams for support. These units were mounted on the floor of the long accelerator building. Concrete shielding blocks were piled along each side and across the top. The klystrons their pulse-control respectively, modulators and were housed in oil baths and high voltage cages, along one side of the resulting - 47 - concrete bunker. @I January 8, 1951, 134 MeV of beam energy was achieved using five kIyOn March 23, 1951, seven klystrons strons feeding 50 feet of accelerator. 70 feet of accelerator were in place and provided a beam of 160 MeV. By April 1951, the Mark III reached 80 feet in length and eight klystrons On that date this arrangement klystrons watts. and were operating delivered 6, had been installed. a beam of 180 MeV. During this time the at no more than half their design value of 18.5 mega- The highest energy obtained with the 80-foot Mark III was about 200 MeV on January 14, 1952. The accelerator was operated at the 80-foot length until May 8, 1952. At that date, the machine was disassembled. The used subsections were cleaned and assembly of the final 220-foot machine was begun (Figs. 0 21 and 22). INJECTOR 0 MARK Ill ACCELERATOR TEN-FOOT SECTIONS K = HIGH POWER KLYSTRON AMPLIFIERS M = KLYSTRONPULSING MODULATORS SWITCHING AND EXPERIMENTAL FIG. 21--Schematic .93-a-* AREAS and plan view of Mark III. - 48 - ___1_..-. --I-_ __-- --- _.____ ._._ __.. . I -.--... .--I.-. --C_-- FIG. 22:-The first sections of the Mark III accelerator, as seen looking in the opposite direction to beam motion (looking toward the injector). The twisted waveguide delivers power from the klystrons to the accelerator tube which is supported by the I-beams. After construction, the accelerator and I-beams were surrounded by concrete shielding. In June 1953, what had been called the Microwave into two parts, atory. the High Energy Physics Laboratory The High Energy Physics Laboratory, Laboratory and the Microwave under the direction W. K. H. Panofsky, 1 was to be concerned with operation Mark III accelerators. Professor The Microwave was divided Laboratory, Labor- of Professor of the Mark II and the under the direction of Ginzton, occupied a new building and continued development work qn ‘Panofsky had first come to the Stanford Physics Department from the University of California at Berkeley in July 1952 to participate in planning for research with the Mark III. - 49 - _---__- --.1- L__ c..--.-----_-^.--- _____- ---.- -- ---- the new klystrons Together these two laboratories and other devices. called the “W. W. Hansen Laboratories By the end of November machine. The maximum klystrons operating. of Physics. 11’ 1953, the Mark III had 21 ten-foot but there were not yet enough reliably electron At this time, operating klystrons sections in place, to power the entire energy up to that time was 400 MeV with 14 Stanford Professor laborators began their investigation scattering using the Mark HI beam. By December ating routinely were R. Hofstadter of nuclear structure with a full complement and his col- by means of electron 1955, the accelerator of 21 klystrons was oper- to yield an energy of about 600 MeV. The injector, Mark III. cess. the source of the electrons, Injection into an electron linear In the Mark II the injector is located at the north end of the accelerator can be a very simple pro- consists of very little more than a hot tungsten spiral cathode arranged to emit electrons with energies of about 80 keV. Although 80-keV electrons have a velocity of only half the velocity possible to inject them into a section of accelerating the accelerating of light. traveling wave has a phase velocity This does not seem so mysterious of light, waveguide in which equal to the speed when it is realized erating fields in the machine bring electrons it still proved very rapidly that the high accel- to almost the speed of light. A high energy electron linear accelerator device where the electrons tire machine. (The traveling is essentially a constant-velocity travel at almost the speed of light throughout the enwaves from the klystrons travel down the entire 1 The third member of Hansen Laboratories, the Biophysics Laboratory, was to come a few years later as an outgrowth of Professor Ginzion’s growing interest in adapting electron linear accelerators for medical applications, radiology, and therapy. - 50 - . accelerator at the velocity of light.) The increase in velocity from near the input end to the output end is extremely increase however is linear along the machine. of the electrons small. The electron energy Energy can be thought of as being . and mass. ’ Increases of energy at low velocities dependent upon both velocity are . almost entirely relationship, . crease. in the form of velocity increases. However, the significant In the Mark II the electrons i factor in accelerator are injected at about half the speed of light. very quickly are accelerating the traveling which pregroups the electrons vary along the length. of at This buncher is just but one in which the internal waveguide, The internal capture. dimensions of the accelerator radio wave. wave can be controlled. are such that the traveling dimensions waveguide are By changing the inside of the tubing and the size and spacing of the annular disks, of the traveling the velocity In the Mark III buncher , the internal wave is less than the speed of light at the input end and near the speed of light at the output end. Thus at the input end, traveling f can continue to ride the crests for more efficient what establish the velocity of the traveling _ close to the So in ~the -Mark III, a “bunching section” is included another piece of accelerator i most of these and many electrons which do not enter the accelerator the proper time are lost. dimensions The wave in near -synchronism. But in this process, diameter “captures” in energy at a velocity Thus the “captured I’ electrons speed of light. physics is the beam or mass does not matter. radio wave, moving at the speed of light, the electrons . using this increases of energy more and more take on the form of mass in- energy . Whether this is thought of as velocity traveling At high velocities, more slowly, the radio wave can capture more electrons, . bunch them iA more accurate statement of electron beam energy is’ E=mc2/[ I-(v2/ce)]’ where m is the mass of the electron, c the velocity of light, and v the elect equation expands to the classtron’s velocity. At low energies, this relativistic ical kinetic energy equation E=i mv 2, plus the electron’s equivalent rest energy. - 51 - properly increase their energy, on the wave crests, first uniform accelerator and deliver section ready for acceleration them to the at near the velocity of light. After leaving the machine at the south end, the accelerated passes into a beam-switching to the left by deflecting area where it can be displaced either to the right or areas through holes in a wall of heavy concrete. Then on the far side of these experimental to reduce the radiation Professor Hofstadter’s of nuclear research areas, a large earth mound serves as level in the surrounding electron scattering programs carried in atomic nuclei, the structure was one of many kinds Hofstadter areas of the was the awarding of “for his pioneering studies and for his thereby achieved discoveries of the nucleons. ” By December 1957, a ninety-foot under construction. campus area. out in the experimental the 1961 Nobel prize in physics to Professor concerning program A high point for the Laboratory Mark HI during this time. of electron scattering It magnets or it can be allowed to proceed undeflected. then enters the experimental a ‘backstop” high energy beam extension of the Mark III accelerator was This extension was completed by July 1960 and from this time on routine operation at energies of 900 Mev was possible. obtainable if all 30 klystrons One CeV was along the 300-foot machine were effective and well processed. During the last half of 1963, the Mark III was dismantled. sections, New accelerator produced to the improved design of those to go into the two-mile chine, replaced the original Mark III sections. By March 1964, the Mark III was . back on the air producing electron beams to 1.2 GeV. Under the direction Professor the High Energy Physics Laboratory W. C. Barber, ma- ate the Mark II and Mark III on a busy and significant of continues to oper- schedule (Fig. 23). - 52 - ~“5**‘--‘----r-s~~,--r. -,<L”PFY~T”.y .“” iw__**_c - .. ..-- .- m_-“._ _. -----*^_..j__ ..- “. ,_, _“. _ ,^ .’ ._ - _” --“------. _ .-.-__ m”““ee.“.,.,u-s.~~.-*uw**r~~ * C. /------ FIG. 23--The Mark III after replacement of its accelerator sections in 1964. In this photograph, all that remained was to replace the concrete shielding blocks on top of the concrete shielding walls. G. Other Stanford Klystron The development and Accelerator of the electron linear accelerator Stanford led to a number of important by-products. have now been built for a number of different different Development sizes for defense applications, and its klystrons The high-power operating at klystrons radio frequencies and including for distant early warning radar networks. - 53 i9 ‘4 L-c * -, . .* ----.-~.er.--.rc-a.-)IDlr- ,--._ -w--..~* -.. _-.---, -.-4~;.r-.--rrr~“ir*(**I-r- - ---.---LeI -..--_ ,‘“*a we.” *--. .C. c _I _..._ iu.I.-.. I.‘. -**UT A number of electron applications. celerator During the mid-1950’s have also been built for medical and other Stanford constructed a lo-foot, 35-MeV ac- for cancer therapy at Michael Reese Hospital in Chicago, a ZO-foot, 60-MeV accelerator a 6-foot, accelerators for cancer research 5-MeV accelerator These machines, and x-rays at Argonne National Laboratory, for cancer therapy at Stanford University powered by Stanford klystrons, in building small accelerators Hospital. are used to generate beta-rays by electron beam target bombardment. now specialize and Many private industrial firms of the Stanford design for medical research. Stanford built several research During the same time period, including two 3-foot, 2-MeV machines for radiation put into use at Oxford University, mental medical research and a 6-foot, by the General Electric 86-MeV research accelerator. one of which was 5-MeV accelerator for experi- Company. In 1954, with U. S Atomic Energy Commission build a 20-foot, research, accelerators support, Stanford started to This machine which became known as the Mark IV, was designed in order to be able to study methods of improving accelerator The Mark IV, under the operational components. of R. B. Neal, was invaluable in establishing and construction for beta-ray In the early 1960’s, the Mark IV was used extensively as a prototype for the two-mile components. methods of design Later for a time the Mark IV was used of linear accelerators. cancer therapy. many improved direction After the two-mile accelerator and for testing some of its machine was well along in construction, in 1964 the Mark IV was dismantled. H. The Beginnings of the Two-Mile The immediate Machine and resounding success of the Mark III in the early 1950’s , both in operation and in application, accelerator. started Stanford thinking about a really big Beginning in 1955, Stanford Professors L. Schiff, R. Hofstadter, - 54 - .-- ...“.l_*..“_“,_ _-__ _Ix ___.._ “) ,__,. ,-“” ,..- _ .--..” . -.. . ‘I ,.._. --. ~“; .,.,. - -.-J---X-~-------~ ~--“r-.~~-.-~-..,-Uolllr-~r*-*--,.c~~~X .-,--v-w, I W. Panofsky , F. Bloch and E. Ginzton met together informally discuss the possibilities of a”Multi- GeV”electron linear several times to accelerator. This group to as the”SHPBG group, “decided that such a machine had good popularly referred scientific justification and that the possibilities should be further investigated. . . To this end,the first”Project Panofsky at 8:00 p.m. on April M Meeting”lwas 10, 1956. In attendance, of the SHPBG group, were K. Mallory, R. Mozley, F. Pindar, held in the home of Professor W. Barber, S. Sonkin, and J. Jasberg. in addition to members K. Brown, R. Debs, R. Neal, From the minutes of this meeting, I1 The purpose of this gathering, the first in a series of weekly meetings, was to discuss plans and form objectives which will ultimately lead to a proposal for the construction of a multi-GeV linear electron accelerator. The participation of the members of this group is entirely voluntary and on their own time as there are no funds available it to support this program.. . should such a program materialize, should be administratively distinct from the Hansen Laboratories and the Physics Department. Professor Ginzton has agreed to serve as Director of the proposed accelerator activity during the design and construction phases, and Professor Panofsky as Assistant Director for at least one year. 2 Professors Schiff and Hofstadter would act as consultants. The primary objective of the proposed large accelerator was declared to be basic physics research. There should be no security measures except to protect personnel and property, no classification and freely publishable results; the facilities should be available to qualified research visitors. . . The following possible accelerator characteristics were listed to orient future thought: Length, two miles; energy, 15 GeV, expandable to 50 GeV.. . ” During the following year, extensive activity was carried out by this study Detailed studies were group3 with the assistance of several other organizations. b* mion is equally divided as to whether the letter M in this early unofficial name of the project stands for Multi-GeV or for Monster. 2 As things turned out, Professor Panofsky soon becam Deputy Director of Project M, a post he held until assuming the Directorship late in 1961, after Professor Ginzton became chairman of the Board of Varian Associates following the death of Russell Varian. 3 During the year, the Project M Study Group was augmented by the addition of the names of F. Bunker, M. Chodorow, E. Chu, D. Dedrick, L. Franklin, C. Jones, J. McIntyre, C. Olson, and H. Soderstrom. - 55 - ~-..---T-T..e-----l.e -,.. -. *- ~Iz-.ae-T ,_,_.~*u*Y.I*I,“---fnl*-lil -.-,-p.-.,_.. ^_. I” _- ._ mx -. ,l-.-ec”*-“,.w,,-~ ,._- -. _r__” -_,ci”n..n.irrrrrw~~ .-_.-* -~--‘-- ~~ --_ ~~a$rrmy-*-- -.-- -., --..r,_.+.-T--v -.-.-.-._-i --_l__.___l__ .--m~ made of the general problems a machine. erator 1 Several special studies were carried structures, poration that would be involved in the construction etc. made voluntary The Utah Construction of such out on beam dynamics, accel- Company and the Bechtel Cor- independent studies of the site and tunnel problems, submitted complete reports on their respective information Planning and cost estimates were made for the construction was generated. and operation of a facility strons which would be required. to design based on its operating of Civil Engineering gineering, Cost and specification and build the huge number of kly- The University (later the Lawrence Radiation Laboratory) information solutions. and of California Radiation Laboratory provided financial experience. and administrative At Stanford, Professors C. Oglesby and B. Page of Geology provided site, geological, civil en- and other information. From all this endeavor, a formal proposal was published. this proposal was submitted by President Commission, On April 18,1957 Sterling to the U. S. Atomic Energy to-the National Science Foundation, and to the Office of the Secretary of Defense for Research and Engineering. The proposal had consistent the very beginning. and impressive The first formal scientific support from almost endorsement of national significance came in 1958 when a panel convened by the National Science Foundation recommended that the project be initiated. Later General Advisory of the U. S. Atomic Energy Commission the President’s Committee Science Advisory in 1958, the joint panel drawn from the Committee recommended the project. the same joint panel, after updating its review of high energy physics, reiterated its support of the Stanford proposal. in the nation. strongly Hearings before Funds to support some of these studies were supplied variously AEC and by Stanford University. - 56 - In 1960, Represented on these panels were many of the most eminent physical scientists 1 and from by the . the Joint Committee on Atomic Energy of the Congress were held in July and August 1959, and in April 1960. A high point in the activity New York . by President during this period was a speech in May 1959 in Eisenhower, in which he announced, I am recommending that the Congress of the Federal Government finance the construction, as a national facility, of a large, new, electron linear accelerator. Physicists consider the project--which has been sponsored by Stanford University--to be of vital importance. Because of the cost, such a project must become a Federal responsibility. In late 1960, under congressional authorization, ated between the U. S. Atomic Energy Commission Stanford University. to perform initial $3,000,000. This contract, engineering campus to house the initial known as “Contract activity Project services M, at an estimated cost of was accelerated. M staff was planned. for the project. Further studies and to acquire architectselected for this (ABA). This joint people from the Aetron Division of Aerojet-General tion, John A. Blume and Associates, Construction A building on the The contractor work was a joint venture known as Aetron-Blume-Atkinson venture comprised Company. Engineers, of 363, ‘I called for Stanford out. Stanford entered into contract design work were carried engineer-management and the Board of Trustees and design of Project Under this contract, a contract was negoti- Corpora. - and the Guy F. Atkinson ABA began work on architectural design and planning for site and building construction. After more correspondence, September 15, 1961 authorized ! - University ization, for the ultimate the total design meetings, and hearings, the Congress on the AEC to enter into negotiations realization of the two -mile accelerator and construction While work on the project cost was estimated continued, tiation between the AEC and Stanford. with Stanford In this author - at $114,000,000. there followed six months of nego- Finally, - 57 - in April 1962, a contract had been executed. In general terms, for the University the contract to design and construct by the AEC. The 480 acres of University built were leased to the government (known as “Contract the machine. 400”) called Costs were to be borne land on which the machine was to be for one dollar per year for fifty years with options for extension. Contract 400 also included provisions l$re-construction of alternative this latter ; 1I research for spending up to $18,000,000 and development. in Besides being used for investigation methods of various design and fabrication techniques, some of sum was used for component testing and development on the small Mark IV accelerator. Ground breaking took place in July 1962, and the big job was begun. - 58 - VII. Biological RADIATION radiation as electrons, SHIELDING damage results from radiant charged particles, Whenever moving electrons ionizing matter. may cause ionization FOR THE ACCELERATOR or they may cause x-rays move on and can themselves strike matter, to be produced. result in the production such they These x-rays of more moving electrons making possible more ionization. If every electron in the SLAC electron beam were to move in an absolutely straight line and if it were to pass through a perfect vacuum, strike matter and there would be no resultant a perfect situation is not realizable First of all, the injection accelerator in a practical of the electrons to collide with. the accelerator striking ticularly accelerator. copper not all the injected electrons can be air and gas molecules for some electrons It must also be admitted that mis-steering occur to result in at least portions tube. purposely X-rays electron linear such direction. Hg; there are always some residual accelerator However, Then, too, a perfect vacuum is never quite -6 although in the SLAC accelerator the vacuum is better than 10 mm in a parallel achievable, at all. into the four-inch-diameter tube is a complex operation; introduced radiation it would never Finally, of the beam colliding and malfunctions with the copper walls of special devices are located at intervals to stop electrons can along the moving too far from the axis of the beam. produced by stray electrons striking the copper walls can induce residual gases in the accelerator or 1 radioactivity in theHousing, par- the nitrogen in the copper of the accelerator, in the air in the Housing, This induced residual and the sodium in the concrete walls. radioactivity . 1 .. The amount of residual radioactivity in the Housing depends upon how long the beam has been on. This residual radioactivity will cause a delay between beam turn-off and entry to the Housing of between a few hours to several days depending upon local radiation levels and necessity of entry. - 59 - Ij __,_--._---- -..“---“p - __ ,,,*‘a.,p+ ipcIsd**e.--w- . *wm**n+grc. . . . . ..---..r.----. .,‘SI __ s ,. ____I I _ _,.. __. ._.- .^ -..... _ I.-- 7-.- Ml”“m*.fi.* “W6^ .e -...--~“IR*r I --m-n” e%+-*F *. remains relatively in the Housing even after the beam is turned off, although with only short half -lives. So radiation and shielded. does exist in the accelerator and must be carefully At the Mark III, the 300-foot-long accelerator is installed a bunker made of concrete blocks averaging three feet thick. along, of course, machine. considered within It was known all that the situation would be much more severe in the two-mile The amount of radiation both to the number of electrons produced by an electron beam is proportiond accelerated per second (the beam current) to the energy of each electron undergoing collisions with matter. and On both these counts, the two-mile machine exceeds the Mark III by an order of magnitude. Some of the earliest design studies for the SLAC machine involved calculations for planning the radiation shielding of its high-energy, A common unit to measure radiation high-current beam. exposure is the “milliroentgen equivalent man” or “mrem . ” This is a complex unit dependent both upon the ratio of the amount of absorbed radiant energy to the mass of absorbing matter and upon the relative receiving biological radiation effectiveness of the radiation and the susceptibility (the chemistry of the matter of this matter to sustaining a biological effect). Although in biological most radiation systems some radiation damage is cumulative. must be related to time. damage is subject to repair, The measure of the effect of radiation Thus standards of acceptable exposure are usually rated in mrem per year. There is no radiation radiation damage to occur. level (other than zero) at which it is impossible Because of the difficulties in experimentation, is as yet no good evidence showing whether very low doses are harmful There may even be some kind of threshold below which radiation Radiation damage is statistical Most radiation in nature. for . there or not. is not damaging. receivedpasses through - 60 - \ *-.e-?.. -w,*so’ ,&‘IFLaww.f,‘-... I- f’. h., 8 1 .._“_, -. ^ __... ..--.s-w-.. -.__ _..I_^ __-.I-.---c-.-.“I-vm.T.d..---*. the receiver with no effect. will cause biological small, harm. this probability But there is a probability If the amount of radiation reduces to “almost” is possible that this has played an important mutations. bombard our atmosphere, producing throughout his entire life, environment. Cosmic rays from outer space continually radiation. Natural radioactive etc. ) also contribute to our from such natural sources is about 80 to The same study also found that the average background rad- 170 mrem per year. iation from such man-made sources as medical and dental x-rays 280 mrem per year in the United States. Thus man is continually in his normal environment amount- of radiation elements in A study by the U. S. Federal Radiation Council’ concluded that the average background radiation radiation and it part in evolution of the species the rocks of the earth’s crust (radium,uranium, radiation exposure is relatively zero. In fact, man is subject to natural radiation through radiation-induced that some of the radiation is about 80 to subjected to of between 160 and 450 mrem per year. This is small enough so that the amount of genetic damage caused by it is experimentally unmeasurable in the individual. can be detected and measured in an individual, (Before radiation damage he must receive a dose of at least 25,000 mrem. ) With the growth of modern science’s activity clear physics, of radiation, organizations resulted installations in the field of atomic and nu- have been established which are concentrated sources In order to protect the citizenry, have studied radiation the Federal Government andother exposure and its effects. Such studies have in the setting of acceptable standards or, more accurately, recommended guide levels for maximum exposures, taking into account that any exposure must be justified in terms of the benefits derived from the radiation 1 activity. “Background Material for the Development of Radiation Protection Standards ,‘I Staff Report No. 1 of the Federal Radiation Council, May 13, 1960, Government Printing Office, Washington, D. C. - 61 - These studies have made recommendations general populace to be considered, involved activity at two levels. First there is the the people not associated with radiation- but who happen to live near such an installation. people, most studies recommend as maximum For these exposure an amount approximating what is called the “doubling dose. ” This is the amount of radiation special installations mal sources. exposure from which would double the amount a person receives from nor- During initial planning stages, SLAC set its own standard of maximum exposure to the general public at only one-half the doubling dose. For radiation workers directly involved in the operation of an installation, most federal studies have recommended that recommended for the general public. a maximum exposure about ten times This takes into account the value and benefits of the work the man is doing while still retaining where the statistical probability planning stages, SIX! workers of damage remains a low exposure level miniscule. set its own maximum permissible at only one-third of the federally recommended During initial exposures for its maximum level. Having set its policy of maximum levels below those recommended federal studies, SLAC carried To allow for uncertainties out calculations in the calculations ing would not be called for, by the for a suitable shielding system. and to assure that additional shield- SIAC selected calculated shielding data that indicated radiation exposures through the shield of only one percent of the permissible maxima, both for its radiation workers and for the general public. The cost of a suitable concrete shield for the two-mile been astronomical, so studies were made of the radiation of compacted earth fill. measurements for uncertainties of radiation Using two different machine would have shielding capabilities methods of calculation, taken at the Mark III during operation, in estimations, SLAC arrived - 62 - utilizing and allowing at the curve shown in Fig. 24. , 10000 b I I I I 1 3 FEDERALLY RECOMMENDED GUIDE LEVEL FOR MAXIMUM EXPOSURE FOR RADIATION WORKERS ( 5000 mrem /year ) 4 . CALCULATED SLAC RADIATION LEVEL FOR 24-HOURPER-DAY OPERATION (45 mrem /year 1 . x e 2 7 IO b 3 3 I id 5 1 0.01 15 I 20 .’ I - 25 EARTH SHIELD I 30 THICKNESS I 35 ( FEET ) I 40 45 493-30-A FIG. 24--Calculated radiation levels outside the accelerator’s earth shield. As the curve shows, the calculated radiation foot-deep earth shield around the accelerator the recommended maximum would be less than one percent of eLxposures. The fact that a full-time would only be on the site for less than one-third . level at the surface on a 25- reduces the exposure even more. The placing of a fence around the accelerator worker of the time (a 40-hour week) . 500 feet from the radiation shield takes advantage of the natural reduction of radiation results radiation withdistance. This in an exposure for the general public of less than one percent of the - 63 - doubling dose (even if the general public spent its entire life leaning against this fence). None of the above calculations took into account the fact that the accelerator is inside a housing made of concrete walls between 18 inches and two feet thick. The extra shielding provided by this concrete is an added bonus above and beyond that calculated for the solid earth shield. beam turn-on confirmed Table I summarizes Measurements of radiation made after the general accuracy of the calculations. these figures and shows the various recommendations and standards . - 64 - I TABLE I ANNUAL RADIATION DOSES Per Capita (mrem per year) General Public 30-year Individual Average Radiation Worker (40 hrs /week) . Recommended Guide Levels for Maximum Exposure - National Committee on Radiation Protection (a) 5000 Atomic Energy Commission(b) 5000 500 330 Federal Radiation Council (‘) 5000 500 167 Stanford Linear Accelerator Center Standard 1500 100 100 . 330 500 - L i -1 -- Natural Radiation (’ ) (Cosmic Rays, etc. ) 80 - Man-Made Radiation (‘) (Mostly Medical) 80 - 280 170 (a) “Permissible Dose From External Sources of Ionizing Radiation,” National Bureau of Standards Handbook 59, September 1954. (b) AEC Manual 0524-02 -F. (c) L “Background Material for the Development of Radiation Protection Standards, ” Staff Report No. 1 of the Federal Radiation Council, May 13, 1960, Government Printing Office, Washington, D. C. - 65 - VIII. Two related investigations THE SITE were carried out during the early planning days. One. was for the selection of a suitable site. The other was for a construction configuration to result in an Accelerator Several methods of construction requirement of a Housing were considered. was for two 2-mile-long structures, itself and one to contain the klystrons two structures were to be separated ing. This double configuration maintained, serviced, Housing under 25 feet of earth. and the accelerator penetrations proper in the in the earth shield at tunnels bored through a hilly area was one method considered. of a parallel one finally Connections be- along the entire machine. Another was the boring of one tunnel for the Accelerator struction in the one structure in the other structure. other were to be made via interconnecting Two parallel The so that equipment could be operated, and adjusted by personnel tween all the equipment in the one structure intervals equipment. from each other by 25 feet of earth shield- while the beam was on in the accelerator somewhat regular one to house the accelerator and associated auxiliary was required repaired, The general Housing with the con- building on the surface of the ground. A third plan, the adopted, was to excavate a trench to the elevation of the floor of the proposed Accelerator Housing and to construct that Housing in the open trench. Then some of the excavated earth was to be dumped back into the trench after the Housing was constructed. until a 25-foot-deep on top of this fill, This fill was then to be compacted, shield existed. parallel Finally, to and directly Several sites were investigated, property the second structure was to be built over the buried Accelerator Housing. including three on Stanford University and three on shore lands around San Francisco requirement layer by layer, for a bedrock foundation, Bay. Because of the the selection narrowed to the Stanford - 66 - ’ . Economic construction sites. considerations eventually led to the final selection of the “Sand Hill” site. The site of the Stanford Linear Accelerator University (Fig. Center occupies 480 acres of land, leased to the Federal Government, in the Stanford foothills The site is connected with the San Francisco 25). major highways. The future Juniper0 San Jose crosses the accelerator area Bay Area by several Serra Freeway between San Francisco and at about mid-length. UNIVERSITY FIG. 25--Location of the Stanford Linear Accelerator Center. - 67 - --- _ -_.. .‘~.C”‘“~~~.5-~~1,--.. _- _I_- _ .__~ _. . ..- .-----_ -._1-.,.-.---_-- - -. ---,- -.-,. ” .-(-,-,.-..-..l*“t-(“l-~.rr~” _. _-__,._ r,r---.r)rrw- . _- ._“,_ -.., l...” .-_,. _..... ,, ,-.-. pewwWWM-l” ,. ^--_- The Stanford foothill area is a belt of low, rolling the alluvial plain bordering San Francisco Mountains on the west. The accelerator feet above sea level, foothills, lying between Bay on the east and the Santa Cruz site varies in elevation from 200 to 375 whereas the alluvial plain is less than 150 feet above sea level and the mountains to the west rise abruptly to over 2000 feet. The site is bordered watercourse in part on the south by San Francisquito draining the foothill med to form Searsville belt. Creek, a major The headwater area of the creek is darn- Lake. The entire Sand Hill site is underlain by sandstone and claystone. rock on which the western half of the accelerator The bed- sits is of Eocene age (over 50,000,OOO years old) and that under the eastern half is of Miocene age (over 10, 000, 000 years old). On top of this bedrock at various places along the accelerator alignment are found alluvial Pleistocene deposits of sand and gravel of generally age (1, 000, 000 years old). unconsolidated earth materials At the surface is a soil overburden of averaging from three to five feet in depth. The trench for the Accelerator Housing was made deep enough so that the Housing would rest on bedrock except in a few places where the Pleistocene alluvium was unusually deep. tions. One of two things was done at each of these loca- In some cases, the alluvium was over-excavated pacted earth. and replaced with com- In other cases the alluvium was mechanically In three other places, existing open valley floors lay beneath the level of the excavated trench. Here too, specially . pacted to the necessary density. There are no historically preconsolidated. selected earth was placed and com- active earth faults crossing the accelerator . site. Several faults cut the Eocene and Miocene beds and at least one cuts the Pleistocene alluvium, nearly a million but there is no evidence of movement on any of the faults years. - 68 - for The nearest large active fault is the well known San Andreas Fault, whose movement in 1906 resulted in the catastrophic This fault zone runs nearly perpendicular San Francisco to the accelerator boundary is about a half mile away from the accelerator’s earthquake and fire. site, and its eastern western end. During f i, f ?1 . the 1906 temblor, area occurred. structural damage to inadequately constructed However, the Searsville Dam, which is within a few hundred suffered no damage at all. yards of the accelerator, Earth strain is known to be accumulating cause this elastic deflection on the accelerator buildings in the along the San Andreas Fault. Be- along the fault could be causing strain accumulation site, field investigations of possible earth movement were made on the site. To measure vertical alignment, period. movement, located at depths of 30 feet. Observations Total differences than one-eighth in vertical - inch. To measure horizontal parallel bench marks were established along the to the accelerator a cyclic way, first l/4 movement of the site earth amounted to less movement, twelve alignment stations were located The maximum horizontal alignment. over an 18-month observation deviation noted period was at one of the stations which moved in inch north, then l/4 inch south of its original All other stations exhibited less movement. the least movement, were made over an 18-month position. The eastern half of the site showed in the order of less than l/8-inch departure from the reference line. These extremely rock foundation, minor earth movements, together with the predominant made the site suitable for construction next step was to build an extremely strong reinforced excavated trench to house the machine. - 69 - of the accelerator. concrete structure . The in the IX. ACCELERATOR The extreme requirements ing the accelerator resulted large construction projects for strength and linearity in the accomplishment lO,OOO-foot-long accelerator peded and undeflected, line. of the structure of one of the most exacting which passes through the 4-inch-diameter, tube, is less than a half inch in diameter. this beam will travel in an absolutely Unim- exactly straight The hole through which the beam passes on its two-mile inch in diameter. hous- ever undertaken. The electron beam itself, i HOUSING CONSTRUCTION trip is barely 7/8 So that no part of the linear beam will brush against the edges of the passage holes, the specification was made that the accelerator pipe over its entire length must have no more than %0.04 inch total deviation from a theoretically straight line. It would be impossible a stringent linearity to build a single rigid requirement. separate 40-foot-long modules. two neighbors via flexible Therefore, structure of this lengthto the accelerator couplings, much like accordian bellows. jacks permit lowered, This adjustment or moved to one side or the other. alignment if necessary. often and to permit has been built in Each of the 240 such modules is connected to its each coupling point, adjustable worm-screw mitted the accelerator such to be initially Beneath that point to be raised, mechanism per - aligned after installation and permits later To keep these jacks from having to be readjusted very them to be of uniform it was necessary to build the Accelerator size and of realistic adjustment range, Housing very straight. necessary to build it very strong in order to retain the initial It was also straightness for years to come. The contractor accelerator was first was given the initial aligned, alignment specification that when the the floor of the Housing must be absolutely straight, - 70 - . permitting no point to be more than four inches above a perfectly etical reference long-time more than one-quarter that no point along the two-mile inch in any go-day period throughout theor- He was given the line and no point more than two inches below. strength requirement straight housing move the life of the accelerator. These requirements and extremely meant that the trench floor had to be extremely straight compact so that it would not sag during and after construction. They meant that the Housing had to be a single rigid concrete structure ting no points of permissible permit- bending. They meant that the Housing had to be very strong so that as 25 feet of earth was compacted above it, it would withstand the resultant forces and remain straight. They meant that the earth fill, in the three places along the alignment where the trench floor had to be built up from valley bottoms, had to be compacted to a high density to transmit tively to the bedrock supporting the majority the Housing load effec- of the Housing in order to minimize Housing settlement. All these considerations resulting from the cut-and-fill had to be applied to all the different technique of construction (Figs. configurations 26 and 27). In some places, the Housing was placed in the excavated trench and filled over to the original ground level where the Klystron Gallery was built. When a portion of the alignment crossed a valley floor, over-excavated hill ,, . that floor had to be so that a hill could be man-made of select fill. This man-made was allowed to settle under its own weight until it was compacted to bedrock density. Then the trench was excavated through the man-made hill and the Hous. ing constructed therein. The final fill on top of the Housing brought ground level back to the top of the man-made hill for construction - 71 - of the Klystron Gallery. _______--------- *i------ BALANCED ------ -_ CUT- FILL SECTION NET FILL SECTION ------ ------ -------- NET CUT SECTION “,“,,C<,’ n* y $.‘? ; El SELECT FILL ( COMPACTED TO 95 % OF MAXIMUM DENSITY, ASTM D-1557 UNCLASSIFIED FILL ( COMPACTED TO THE ABOVE SPECIFICATIONS ) SELECT FILL REPLACING UNCLASSIFIED MATERIAL REMOVED BY OVER-EXCAVATION POROUS BACKFILL-( f ---------- i FIG. 26--Typical In many places, - cross PEA GRAVEL ORIGINAL GROUND sections of Accelerator the original 1 493-33-1 Housing and earthwork. ground level was at a very high elevation so that a very deep cut had to be made. The Housing was built at the bottom of the deep cut and again filled over with 25 feet of compacted earth. Gallery in these places is below the original All construction i The Klystron ground level. started at the west end of the site. As soon as several thousand feet of bedrock floor had been opened, and while more cut-and-fill work proceeded eastward, The Accelerator foot-thick construction of the Housing began. Housing is a 10, OOO-foot-long concrete box with 1-1/2- walls and 2- to 2 -l/2 -foot-thick - 72 - roof and floor slabs. The interior of . : .i. \~$gi . -. ,, h -:-;J.. ‘, ~\’ ‘_ . ‘; <* r. :‘; * - . . . FIG. 27--The two-mile-long cut-and-fill in mid-1964, looking west toward the Pacific Ocean from the initial excavations for the two target buildings. the long box is 10 feet wide and 11 feet high. 4000 tons of reinforcing Imbedded in the concrete is nearly The Housing is a monolithic steel. from end to end, containing no expansion and contraction The Housing was built in 80-foot-long poured first. The intermediate ready cured sections. This permitted cracking big problem Alternate In this jointless sections were the concrete of the later sections to flow resulting in the construction in an overall continuous Housing. of the structure inherent in the curing and drying of concrete. much of this cracking joints. sections were poured later between pairs of al- and bond to the existing sections, The first sections. concrete structure was the shrinkage . In normal concrete work, tendency is absorbed by expansion and contraction structure, reduce the shrinkage factor. joints. the most effective way to reduce the cracking was to To achieve low shrinkage, - 73 - the concrete mix was carefully designed and mixed and the pouring and curing were closely controlled. It was found that the use of crushed, gates, with samples pretested specification. was es- To reduce the effect of temperature changes, of the concrete poured was maintained between 40 and 60 degrees During summer night-time Fahrenheit. or granite aggre- to insure low shrinkage characteristics, sential for a low shrinkage mix. the temperature high quality limestone pouring, ambient temperatures met this ice often had to be added to the For daytime summer pouring, Adjacent to the on-site concrete plant was a 20-ton-perday concrete mix. ice plant which produced 150 pounds of ice per cubic yard of concrete on hot days. The first vinyl chloride step in making ready for a pour was to lay a 0.02-inch-thick membrane in the floor of the trench. poured over the membrane to protect Then a 3-inch sub-slab was it during construction (Fig. 28). ( y- \:-, - i- & :,” ’t’ -cy “‘..&,i’t;,, “p&-y A---- _ *.I~L-r,r,A;-. - _ ..,.4?y: ----.-z -_ - ---- ‘T- , ; .fg&. ,- ,’ -I’.? -Cl .7 e- _. 4 key._J7 -7. &, r: -; qs- ‘- --- --- , i \ -.‘-ki\.! . 1’ .i, / __,,; ‘&. ,/.- ---“i--_ ,’ ; .( ’ ‘T-C - \~, -. ‘l ...~,-%.,. I_ ‘\, ‘-x ‘y.‘x. ‘x. ‘c”b, ‘. 1.. ,, 1,. -’ f _ ‘A_ ‘i, ‘-.. ” :r;, -ye. JI ..r’- ‘;- - _ / ---L-..- ’ --. _. Ji’ , ,I ~,:, , ,, ,/ \\ Next the of l/8 inch. steel forms for the Housing were put in place and set to a tolerance - poly- i > --.~___ __ )i-.r:--Pr ; j’ I ,., *,.I .J / -. t-9 1 ;- * ,)... , -3 i Ib__ FIG. 28--Sketch of the sub-slab laid before Housing construction began. !/ I : ----i. ‘-1 “ ..,~, - 74 - _ ‘j’.,*:-1, I- _- --;,. I, i. .”;~?j ! ’ ’ .- ;- T~~~~~,lk~__~:; -. y’-- -‘. 7 “+‘\.*982. : .. With the forms in place, the walls, Housing were monolithically (Fig. floor and ceiling of the 80-foot section of poured around preconstructed reinforcing steel bars 29). FIG. 29--Sketch of the Housing under construction in the trench. The vertical structure is one of several equipment accessways. After the concrete had set, the forms were stripped away and water pipes with spray nozzles were placed on the sides and top of the new Housing section. For the next fourteen days, the green concrete was subjected to a “fog” cure. Once the curing was completed, the fog spray was used as an evaporating coolant to keep the temperature of the Housing low until the embankment fill material type could be placed upon it. When the concrete was cured, . an adhesive sealer was applied directly the concrete surfaces and more plastic around the sides of the structure. to membrane was sealed to the top and The top and side pieces overlapped the sheets - 75 - placed beneath the sub-slab to make a watertight In order to reflect seal around the entire Housing. heat away from the black polyvinyl chloride until the embankment fill had been placed and to protect the membrane during backfilling, of white fiberboard To permit insulation moisture were placed around the top and sides. drainage, a porous back-fill both sides of the Housing in the remainder the job of placing layer after layer the Housing, o pea gravel was laid along of the trench (Fig. Then began 31). fill had been completed and compacted (Fig. cracks were searched out. These cracks, tion joints between sections, 30). of earth around the sides and back on top of each layer compacted to bedrock density (Fig. When the 25-foot-deep sheets which occurred 32), mainly at the construc- were pumped full of an epoxy grouting. This epoxy formed joints as strong as the concrete itself. .I ” ‘ */ ’ ~- ‘: : .*r&rFw - , _ .-- .j :‘4 . 2 I _ .. I -I .; .- ‘I i ‘: T. & ’ .,d *, J+J ‘,! “-9 i. L . I w . ~~ ..:’ . .. . & * :: . . -?a!+. . : ‘I%” e -q ,a .-_ . , i’ ” ., . FIG. 30--The first few sections of Accelerator Housing with the pea-gravel back-fill covering the protective Celotex sheets. - 76 - r “V .-, --“.--..r--_X____rr -~___,~_,.” ,_,_.._,__- L ^,-, ----..- _“.. __-.- I.-. - -1.(1*--^ . ..-.- II--- --T-XIII- . FIG. 31--Accelerator Housing construction continued eastward while we_stern portions were being covered with compacted fill. L--M’:‘ -r-2 -_ .:.Z.--;-* ,_ .-r- . . -:.y,.- -, ‘7 : ye--. .._ i ~-. - 473 -. 23. . -%c:: ST- i. ;;j ‘...&y. ._ -,. j ..: --.-_ arnr t -._ ‘< -c /,..-~. i, _ r;/ ._, < -“:‘;,-,. 7...+.- _, ;: I’ -_ -EfW .. . I L r 1” ;’ ~ .!,..h< y ’ $?.“_,~sT’.A---s.. e.2 ,_I,, _ i- .i :a ;_ ._ --. .‘. .- I- ,_r *; ._. h -i i ’ --~“.:..m_ --‘& -. ‘- ,.. . -- ,r / _,- ...,a_-- -c ._ I 8 k’ ‘. .._ *- . .-. ._ /.‘- /<‘, ‘: . -I 1% . ,$\ RI_ ,., ..._(l . i.- . tB, - -.. -;?-4 FIG. 32--Sketch of the completed fill over the Housing, showing the top of several of the penetrations leading to the Housing. - 77 - .d During accelerator operation, 90 degrees Fahrenheit the Housing is at a temperature due to the energy dissipated in the machine. the concrete to tend to expand. The epoxy grouting resists enhances the structural Finally, 33). The Klystron divided into thirty frames (Fig. vides for resistance 34). A structural are resisted roof are noninsulated steel longitudinal seismic forces. by the structural m Further such resistance ; .>r , _ a,‘. is Seismic forces in the rigid frames. The walls and (Fig. 35). .f .3 3d ??eL-.,:I_ ._ ; s-<---+&- , --?gj ‘+- 3 : -. -. , : %.. ...’ ‘. . . J . ,; . .. . .. 5 ‘1’ *. .;.! , ._ ‘+-. 1 ; _ ;> .I . a\. bracing system pro- fluted metal panels with no windows or skylights ke;*y;l ‘.’ b .F:-ET;,. 2. 2‘. ,,-I ,. -. : .’ Ici, . L‘ ’ ! ‘4’ ‘b , :i i structural-steel-framed consists of a rigid steel frame every ten feet with to longitudinal direction above the separate from each other to allow for ther- provided by concrete shear wall panels in each sector. transverse the concrete. Gallery was constructed Gallery is a single-story “sectors” The structure mal expansion. transverse Klystron This causes this expansion and thus of the Housing and pre-stresses the on-the-surface Housing (Fig. building, integrity well above , _._ -I’ . t b. _. . . . .- -_.’ ,“1. \ ‘,“ -:’. . . . _ -.,: _-._ ._’ ‘*> ..I ., ” ~ ’ *, -.I::,;. f ‘,,.,’_ ..‘....L 4 ,..;;.:i,‘.;.:;:‘l.b.~i a~,,;.*.\;+~.Y;;:.;Q-.&;;&r;;.:.<<: .I*~,.j-~.;.:=i,~l~~~ i.’ . .. . . FIG. 33--The western end of the completed Accelerator Housing with 25 feet of compacted earth above it and construction of the Klystron Gallery begun. - ‘78 - -Y__rl.,.“--vi-ll- .I*.... I q -“.“.w~.,-.. -..,--) . . ..- ..I ,. ..- ,.- _“. ____,-_ __ --,---.- . I . . * i c,. _.” -, -.. . . *. + ; ,. .j .._. ..- ’ ’’ I... I... ’ . . r i . .. .. i _ _.“..- .;.; .. , .- k( kg -* -* .::.-.::.-- 1* --3. 3. P -_ _._ , ,‘ 1: *... r. *.-- 1.1 ._ I I Ir FIG. 34--The , framing of the Klystron Gallery. -i . “\ ,,* :,* . ‘,. , .. \( .,,.. 7 ., &.. - ,II_ ;i, FIG. 35--Sketch - of the Klystron #‘.’ (I ‘ (( __ . .*t” Gallery under construction. - 79 - .L.Y . .i’ . Removable roof sections provide access to the rigid structures equipment in the Gallery to the accelerator connecting the in the Housing via the penetrations in the ground. Alcoves along the north side of the Gallery contain instrumentation trol equipment for each sector. other periodic mechanical Alcoves along the south side of the Gallery house and electrical Besides the approximately equipment 2-feet-in-diameter At one place in each sector, I..., t‘ I_ _ 36). penetrations in the ground, on the south side, a vertical These are 3-foot-wide accessway has been constructed. .a* -\~-‘ d (Fig. there are several accessways from the Gallery to spaced usually 20 feet apart, the Housing. and con- >if. > - .-.*. I _ . ..-~.;-.>I-. manholes, man 25 feet deep, .._ - .., L ;: k 1 , &: 1. -. ,, *. .i’\. .j _: -._ .h i .i . f _ ‘?. ‘ . -:. .-. (. i .. I c . .$ it‘. . . ‘I *, \ FIG. 36--The complete Klystron Gallery as seen from the injector or west end. - 80 - _I__ .._- “_ ,--- e.._yc~ e...% ._.“.Ix .__._ .m_, ‘-- -.-- -- ^. __ ___.. -_. ,l --e_. -.” _e.. ..---^ -_-- __” I. . ..“_ equipped with wall ladders the machine, larger ( Fig. 37). In addition, at a half -dozen places along accessways have been constructed to permit apparatus to be raised and lowered into and out of the Housing. trations equipment and All these pene- and accessways are capped and are offset from the accelerator not to act as passageways for straight-line As construction of the accelerator radiation of the two 2-mile-long and auxiliary in order from the accelerator. structures proceeded, installation equipment was begun. .“y-“.-.“?.r--,-- ..e. ..,; I .‘, y‘ ,yi; * 9. P. ~ .r?, I , .-a-. -_ .' : 4. .: : .A. q:‘?.fl: 1, -i : .y”.Ay+“* i’ ), q '.,A rii “&$I ‘., 8 z '* i ', ', ; J ~. ? .: ;.,, v, ;--T j 1 t ; ., ’I., ‘I “, : i . s ,c L ,!’ i I ,, ,:* i. ), : \ ;~~~~,‘~‘ :‘: i f,-. ‘), / I’ 1.’ !’ . ,,‘ c,*i,,I .: :’1 c FIG. ST--Cutaway sketch of the Klystron Gallery and Accelerator Housing showing interconnection penetrations and one of the man accessways. . - 81 - =wT+?F -..-.P ---iii y rea.e..~..s.1.a‘* ---_-.-___--l_--_--~--1 V-.*^.rwui.nv--e.- .,,N-enee--m- _s_lc___c__I e ~,w-~.xXrrXIC*~~- .... ........... .... 1._- 1-3w-., .... . ,( .. .*a,<& . ,M . “dw-*-” X. THE ACCELERATION The basic unit of the accelerator into four lo-foot-long underground “sections. Housing. by one high-power proper is a 40-foot-long “module” divided ” There are 240 such modules installed Radiofrequency klystron SYSTEM amplifier power to each 40-foot module is supplied tube (Fig. 38). The klystron pulses of up to 24 megawatts of radio power at the microwave megacycles per second. Directly above the klystron, output power is divided into two halves. carried down through the 25-foot-deep piping in each of the two penetrations in the produces short frequency in the Klystron Thus 12-megawatt of 2856 Gallery, this pulses of rf power are earth shield via rectangular waveguide associated with each klystron. r A. / ,’ FIG. 38--Two of the 240 forty-foot-long accelerator stages. - 82 - . w.__?_ I-m-.*-. -^.*- ----.- - .----___ -..__ _ _ _ -___ At the bottom of each penetration, the rf power is again divided in two so that 6 megawatts of power is available to feed each lo-foot ator. This high power radio wave enters the typical at its west end, via a coupler, and travels lo-foot of light. a the radio wave and ride it for ten feet, absorbing energy. i . The electron beam from the previous Therefore, the radio wave has lost sufficient water-cooled of this energy loss wave heating the copper walls of the accelerator Meanwhile the accelerated again through a small terminal electrons This power splitting hole, and enter the next lo-foot acceleration. scheme serves the purpose of equipping the accelerator so that if in future it becomes desirable to increase the energy of the accelerator, all that need be done is the adding of klystrons. For instance, four klystrons could be placed where there is now one, and the entire 24-megawatt each could be delivered to just one lo-foot to as “Stage II” (Fig. The actual accelerator section. 39). interstacked tube assembled from with over 80,000 copper disks (Fig. 40). . by SLAC from extremely pure copper and disks were fabricated stock, the cylindrical pieces sliced from long copper cylinders, - 83 - _.-_ i_._- C1lI-.r..C..m the disks cut These pieces were then machined to tolerances from large pieces of copper plate. .x__c___ output of Such a possible future phase itself is a four-inch-diameter over 80,000 copper cylinders These cylinders is taken continue their a new radio wave receives them for another lo-foot has been referred pipe. ) section at its east end and is dumped into and dissipated by a copper load. easterly trek, length’where energy so what remains of the radio wave after ten feet of acceleration out of the lo-foot enters are caught on the crest of that it is no longer economical to continue acceleration.(Most is caused by the traveling section section of the accelerator this next section through a small hole. The electrons After ten feet of acceleration, accelerator east through this section at the speed I 1 f i . 7 section of the acceler- -^.- ~ - -.,. -....-w.~-xv.--“-~. -, within 0.0001 inch. To maintain such machining tolerances, an air conditioned room with a temperature-controlled degree Centigrade) p---I 40ft I I --j I I I STAGE I I r I Ioftt- I 1 ELECTRON GUN / STAGE II KLYSTRONS ACCELERATOR 493.32-A FIG. 39--Diagram of the present klystron-to-accelerator (Stage I) and of the possible future configuration i of a ‘---ACCELERATOR \ELECTRON GUN L (to within a quarter coolant oil flowing over the part during machining, KLYSTRONS I cutting was done in c7 “* I I+ , I i Ir *- \ I \ f ;- J / c1. ‘, configuration (Stage II). 1 cl--: . x* c 1 ,/ L /Ai Fig. 40--Copper cylinders and disks making up the four-inch-diameter, two-mile-long accelerator structure. The thin wafers are alloy rings for brazing the cylinders and disks together. - 84 - --~-__ --..-- _--__.-,.__I s -.N^I_-. m”,%.*“-,>“. *“*.. ,-.-I - ,-. - .” ._..” ..-,.--v.-, -- *..m”..^-I.“I---” .- After sufficient disks and cylinders assembled with brazing copper-silver Then the entire ten-foot flame, . a stack ten feet high was alloy washers between each pair of pieces. section was brazed together to form a solid copper unit. The brazing was carried of disks and cylinders. were machined, out using a split-ring This ring burner, burner which surrounded the stack which was fired by an oxygen-hydrogen was started at the top of the stack and moved slowly down. As the burner passed each joint, Following the brazing alloy washer melted and fused the pieces together. the burner down the stack was a water-cooled chamber in which the brazed section could cool. The ten-foot section was completed when an array of small copper tubes had been brazed to the exterior of the section (Fig. 41) in a separate pit furnace. These small tubes are for passage of temperature-controlling water during operation. % ,.e * _ - _ &-rrw. 3 FIG. 41--One lo-foot section of the accelerator pipe showing the input and output rf couplers at each end and the small center-fed pipes forming the accelerator temperature control jacket. - 85 - Every standard lo-foot However, slightly. section of accelerator within each lo-foot Thus the first sections, section, the disks and cylinders predecessor. length, culations and experiments each succeeding cavity is smaller In all the early Stanford accelerators, ties formed by the disks and cylinders were identical within a lo-foot takes place along in a decrease of rf energy along at any point depends upon the magnitude field of the rf wave along the axis at that point. through a uniform lo-foot section, along the section, which the cavities would permit. the electric the electric As the wave travels field strength decays. This means the field strength is less than the breakdown limit with succeeding cavities made smaller, However, field remains constant at its peak value, permitting to the electrons. inside diameter cylinder. one-fourth smaller internal In each lo-foot of the last cylinder of the first section of the two-mile is a little The diameter machine, over one percent smaller earlier the than that of the small hole in the last disk is nearly than that in the first disk. Sections employing this gradually conical design’ are now installed machine. a greater energy The incorporation in both the Mark III and the of these new sections in the Mark This design is referred to as “constant gradient” as contrasted “constant impedance” design. , III resulted in as much as 20% more energy per foot being given to the electron 1 Cal- would result by varying the cavities section, resulting The amount of energy transfer that further in size in the section. of energy from the rf wave to the electrons the entire length of the lo-foot of the electric all the cavi- length. The transfer the pipe. than during the early stages of planning for the two-mile machine showed that improved performance two-mile vary in dimension the second in each section is the same size as in all other sections, its immediate tapered to every other. cavity in each section is the same size as in all other and so on. But along each lo-foot transfer tube is identical beam. to the - 86 - ..% :* -m-mmm-,e. v “..-e.... .- .,I^ _*_ .I._.-__ .w -_. ..,- ..,__“.~ -,____ *- ___I_- Some of the final dimensional tolerances of the cavities in the inside of the section must be held to f 0.00005 inch, better than can be achieved during machming . A final step in the fabrication cal tuning. of a lo-foot the cavities In the manufacture, section, then, is a mechani- are made just a little bit oversized . to permit . final sizing by deformation through the finished ure the velocity lo-foot section. or squeezing. A plunger reaches into the section to meas- of this wave through a cavity. cavity are not exact, the radio wave travels automatically A radio wave is passed If the internal dimensions at the wrong velocity. of the Slow moving, driven pneumatic plungers then gently press against that cavity at four equally spaced points on the outside. When the radio wave is traveling This begins to squeeze the cavity. at the exact velocity desired, stopped and that cavity is tuned. Each cavity in each lo-foot the squeezing is section was tuned in this manner. Next, four lo-foot sections were assembled on top of a 40-foot-long num pipe two feet in diameter pipe is to serve as a girder, When all the auxiliary all laboratory (Fig. 42). The primary providing rigidity function of this larger and strength to the overall components had been assembled on the girder adjustments and alignment had been performed, stalled module. module. and after this 40-foot module was slowly hauled out of the shop and down to the Accelerator it was placed on adjustable supports and flexibly alumi- Housing where coupled to the previously in- Over 240 modules were placed in the Housing in this way (Fig. 43). At the peak of fabrication and installation, SLAC was producing one 40-foot module every working day. - 87 - and installing . FIG. 42--A completed 40-foot module on the transporting rig ready to be taken to the Housing for installation. The accelerator is the smaller, uppermost tube. The large tube is the support girder. The small dark tube is a manifold for the vacuum system. ““V .-ssy; _, ’ ,.‘s- - “‘Y -,. i ‘- _. _ i 1 I . .". '\ - I --..., ‘, i .. .a I 9 i L i * j _. .I.. s i ~ ^ -------.. ;’ : L., ! i.. i ,c .e 1, .,/ .J j. I’ - -4-.mmaz% ^T 7 i,.i :.- * ,.a .I- 1 j .i _ ~’ - ,I ’ ,;e _ * L .r ; i b _,” & ..- :. -- c . t ;r i : FIG. 43--The interior of the Accelerator Housing after installation of the accelerator. - 88 - ----___ __^_jII,-..-... --- .” _-.. 1 __.%- jTm*_*_-cl----. “-%- XI. A secondary, AUXILIARY but not inconsequential, advanced devices as the two-mile refers to as “technological by-product accelerator of the development is what the Federal spinoff. ” To accomplish signing and building a complex installation nology, many supporting SYSTEMS requiring the formidable Each of these devel- and is usually applicable to other areas A great deal of research has gone into developing the several aux- systems required these auxiliary result, task of de- systems and components must be developed which them- opments broadens the ability of industry iliary Government advancing the state of tech- selves are advances in modern techniques and capabilities. of endeavor. of such to make the accelerator a functioning reality. Most of systems and their components were supplied by industry. new techniques have become available to industry As a to apply to expansion of their capabilities. A. Injection Several requirements were placed on the design of the assembly which creates the electron beam in the first place and molds it into the proper form for acceptance by the accelerator. all produce electrons Then the injector electrons in sufficient This assembly, the “injector,” must first quantity to supply the required of beam current. must focus and aim the beam so that at least 8O%.of the inserted reach the far end of the machine without striking erator tube. This is because such striking the Housing and would thus necessitate sign requirement. Next the injector the walls of the accel- would cause excessive radiation reducing the beam current in below the de- must bunch the beam; that is, the electrons must be speeded up and slowed down (as they are in a klystron) so that the appear- ante of bunches will coincide with the crests of the radio waves in the first accelerator section. Finally, the injector must preaccelerate - 89 - the electrons up to a sufficient velocity where they are capable of being “caught” by the accelerating radio wave crests which travel The producer of the electrons at the speed of light. is a relatively standard “electron electron gun is much like a triode vacuum tube. A hot-wire surrounding cathode sleeve of some material, is a good emitter of electrons. cathode. These electrons filament such as thoriated heats a tungsten, which The heat causes atomic electrons to “boil off” the form a cloud in space around the cathode. An anode (a plate having a positive voltage ) attracts the electrons Most of the electrons pass through an aperture moving in the direction gun. ” The of the accelerator. in the proper direction. in the anode and form a beam A third element, called the “grid, ” lies between the cathode and the anode. This is a fine mesh screen which will allow the electrons to pass from the cathode to the anode unless a negative voltage is connected to it. Thus the grid can act as a switch, turning on and off the I this is done-.at SLAC to form the pulses of electrons. electron flow. In-fact, By controlling the amount of negative voltage applied to the grid and controlling the timing and direction of that application, beam pulses are controlled. characteristics. the rate and direction of the electron This allows beams to be formed of various desired In fact, alternate bunches can be made to differ from each other for varying applications. The electrons from the electron gun have an energy of 80 keV. then enters a “prebuncher klystron.’ Here initial , ” which is a cavity much like the first rough bunching of the electrons This beam cavity in a takes place. This is 1The entire accelerator is “pulsed” so that electrons flow for a little over a millionth of a second between much longer dead times. During this millionth-ofa-second pulse, the electrons are formed into several thousand in-line bunches to coincide with the number of wave crests appearing during that time. 2 Refer to Section VI-D. - 90 - --. .___ _.--_------ nr_--.. __-... .W,,” - _ ,-__ _ ~~-- ,,_. __..-_---. ._...“-.*ll-.-.-- ---I --11. followed by a drift tube, again similar to that in a klystron, lation of bunching is allowed to proceed. lo-centimeter-long buncher a radio wave traveling electrons Next the prebunched electrons internally at three-fourths to an accelerator the velocity of light further and raises their energies to 250 keV. standard lo-foot . similar accelerator the velocity of light. where the accumu- Finally, section where an accelerating enter a section, where bunches the the electrons enter a wave is traveling Here final bunching takes place and electron at energy is raised to 30 MeV. The beam in the injector electromagnet, erator which surrounds the lo-centimeter spot size by a solenoid buncher and the lo-foot accel- section (Fig. 44), aided by various magnetic lenses and steering magnets along the injector. acteristics B. is focused to the proper At the output of the injector, various devices monitor the char- of the electron beam as it is introduced into the accelerator proper. The High Power Klystron Over 240 high power klystron Klystron amplifier tubes are spaced along the two-mile Gallery to provide the radio waves to be inserted FIG. 44--Simplified diagram of the injector, - 91- at regular intervals showing major components. into the accelerator. earlier, These klystrons in Section VI-D. these klystrons have five. However, ity, this cavity is excited. narrowed described instead of having just two resonant cavities, The three cavities between the buncher and the catcher refine the bunching of the electron and fourth cavities work on the same principle stream. As the bunches reach the second cav- Its oscillations narrow the bunches further. The third do this again until the bunches reaching the catcher have been in space and time to result in a near single-frequency amplified output radio wave. The high power klystron is installed The cathode supplying the electrons FIG. 45--Cutaway in the Gallery in a vertical orientation. is at the bottom (Fig. 45). The collector drawing of the SLAC high power klystron is amplifier. - 92 - --- - .UII_..__ c_-e.------- _-_.--.---- -w at the top of the klystron. Surrounding the five cavities is a permanent which serves to focus the electron stream to keep it from diverging narrow stream configuration. body and the collector The high voltage (-250 kilovolts) ground potential. switches the klystron klystron The klystron from its are kept at from the modulator, which on and off, is applied to the cathode at the bottom of the via a connection through a ceramic cathode structure magnet is surrounded high voltage insulator. by an oil-filled The entire tank to house the transformer which applies the high voltage pulses. Because the vacuum inside the klystron that in the accelerator output line. is continuously This window permits is a permanently sealed one while pumped, a “window” is required the klystron shipped to SLAC, tested at the accelerator to be evacuated by the manufacturer, site, installed in the machine, removed for maintenance or replacement without loss of vacuum. must maintain the vacuum in the klystron and yet permit megawatt pulses of microwave sputter-coated with titanium. sening the probability power. in the rf The window the passage of 24- The window is made of aluminum trioxide, This has proved to be the best combination of cracking and for les- of the window due to the passage of the pulses of radio power. The design and fabrication most crucial tasks in the program. ment and manufacturing specifications of these klystrons programs was considered to be one of the It was decided to undertake several developin parallel, Successful tubes meeting full have been produced by four outside companies as well as by SLAC itself (Fig. 46). All of these tubes are electrically able, amplifying a radio signal of 2856 megacycles per second to levels of between 21 and 24 megawatts. An installation Gallery is shown in Fig. 47. - 93 - and mechanically of several klystrons interchange‘ in the Klystron EIMAC FIG. 46--Five of the high power klystrons, ready for installation, as manufactured by four different companies and by SLAC itself. ~-_~--~PFRc. ---1-.-- - *. k -2 --s-y-;-~, 9. - ‘F-, - .; I r;;, t; I-ir s< \ ;,I #// L.. l-y ’ _ 4_ I 3; , --’ - t - ’ I I‘ /! iii, ;[ it i: I-’ $L .I.: \. --LL> i 2 -=-A . I/ . 7. -m “A ‘,-1 .s e..,_ .._ ! ;-= ! k-- ‘.5-“-‘5 ,‘- __._.._ - - d ,’ 1 -. .: r,- .-_ .. .. I i L I , ‘8. 2’. P FIG. 4’7--The interior of the Klystron Gallery. The 40-foot installation, with its klystron, is repeated 240 times down the length of the machine. A vacuum pump is shown sitting on the small shelf above and to the right of the first klystron. The vacuum manifold is the long, dark pipe running along beneath the roof. - 94 - , C. The High Voltage Modulator Each high-power klystron must be turned on for 2.5 millionths of a second and then turned off. This occurs at a selectable rate of between 60 and 360 times per second. The device which accomplishes modulator. this switching This is a large cabinet which houses the high current rectifiers to change the supplied alternating regulating circuits klystron. The switching is done by the modulator and components. ing the 250-kilovolt D. is the high-voltage Trigger current to direct current, There is one modulator beam voltage at the klystron switching tubes, and the associated with each alternately applying and remov- cathode. System To control the pulse rate of the accelerator, erated near the injector a master trigger end of the accelerator. nal is sent out to all stations in the machine, signal is gen- This 360-pulse-per-second including the injector sig- and the 30 control alcoves associated with the 30 sectors into which the accelerator is divided.’ Other separate control signals are sent from a central control room to each such station to tell each station which and how many of these signals to accept. Thus one sector may be operating is operating, say, at 120 pulses per second. This means that some electron beam pulses can be accelerated In this manner, by more sectors than alternate several different be produced in the accelerator The trigger strons “interlaced” turn the injector high-energy beam pulses might be. electron beams can at the same time. pulses which are delivered on and off last for 2.5 millionths accelerator at 360 pulses per second while another on and off are shorter. to the modulators to turn the kly- of a second. The trigger This permits section with rf waves before the electrons each klystron - 95 - to fill each in the beam start their trip. Because the beam pulses are less than two millionths because, through most of the accelerator, pulses which of a second long and these pulses are traveling nearly at the speed of light, electrons are physically inside no more than about one-fifth This 2000-foot-long the length of the machine at any one time. bunches moves down the machine, of the klystrons section by section. because the trigger pulse of electron Therefore, must be accomplished in a sequence. of the turning on This occurs almost naturally pulses to activate the modulators also start at the injector end of the machine and travel at nearly the same velocity along the trigger line cable. E. Drive System The original rf signal which is to be amplified orginates in a single rf generator. per-second by all the high-power The output of this oscillator power down the two-mile it to a frequency multiplier. These varactor then, a pulsed sub-booster in that sector, frequency klystron this 2856-megacycle. signal to a power level of about 2400 watts. coaxial line distributes F. remove about four watts the frequency of the rf wave to the final frequency of 2856 megacycles per second. At each sector, plifies this rf length of the machine. of this rf power and deliver multiply which brings this A coaxial cable distributes Couplers in each of the 30 sectors of the accelerator multipliers is a476-megacycle- radio wave. This is fed to a main booster amplifier signal up to a power level of 17.5 kilowatts. klystrons resulting this power to the rf input connectors am- Another of the eight klystrons in about 300 watts of rf drive per high-power klystron. Phasing System The electrons vious section, in the beam arrive in each accelerator in bunches. In order for acceleration tion, the radio wave from the klystron section, to take place in the new set- for that section must be so timed that its wave crests coincide (are “in phase”) with the bunches of electrons. that this is the case, a semi-automatic from the pre- To assure phasing system is associated with each klystron. - 96 - , Whenever it is deemed necessary to check or adjust the phase of the rf wave from a particular pears klystron, the pulsing of that klystron is delayed so that it ap- after the beam pulse passes by. The bunches of electrons pulse themselves induce small oscillations in the accelerator those which are induced in the catcher of a klystron. The relationship the main drive system. These induced oscillations is de- ence. The output of the klystron is compared to the same refer- is then adjusted so that its relationship is exactly opposite to the relationship In direct opposition, phase, that of the rf wave in between the two is noted. Next, the phase of the output of the klystron reference. much like by the timing of the bunches of the passing electron beam. The phase of this induced wave is compared with a reference reference section, The phase of these induced oscillations cause some loss of beam energy. termined in the beam the klystron of the beam-induced output is properly to the wave to the adjusted to be most effective in making up the energy lost from the beam due to induced oscillations.. When this is accomplished; to produce the maximum G. the output of the klystron acceleration has been “phased” in the beam in the accelerator. Beam Guidance Magnetic fields inside the Accelerator beam to veer from pure linearity. Housing could cause the electron Such fields result from the earth’s magnetic field and from stray fields from mechanical and electrical sate for these, each 333-foot sector of accelerator vertical and horizontal are independently counteract degaussing coils. sources. is surrounded The degaussing currents adjustable for each sector. The currents To compen- by a set of in these wires are programmed (or “buck out”) existing magnetic fields with opposing fields. to Then, to reduce even further the difference field, tube is wrapped in a magnetic shielding made of molyperm- the accelerator alloy material, between the natural fields and the counter which reduces the remaining - 97 - difference by a factor of 10. At the end of each 333-foot sector there is a lo-foot special drift section containing special devices to locate and to guide the electron beam. This drift section includes a magnetic focusing lens, a set of steering beam-position beam scraper, monitor, a set of a beam-profile monitor, regarding any horizontal a and two vacuum valves. The beam-position and vertical a beam-current monitors, magnets, monitors displacement provide information of the beam. The beam-current monitor measures the number of electrons per second in the passing beam. The beam profile is remotely insertable in the beam path and measures the relative of electrons at each point in the beam’s cross-section. monitor concentration The beam scraper permits only the proper central portion of the beam to pass and stops the diverging electrons at the edges; this protects bardment by these diverging the accelerator electrons itself from eventual bom- and localizes radiation The two vacuum valves, one at each end of the drift section, to the scraper area. permit the isola- tion of one sector from the next if desired. H. Support and Alignment As described earlier, each rigid accelerator connected to the next module via flexible module is 40 feet long and is bellows-like couplings (Fig. 48). One end of each module rests upon three adjustable worm-screw supports, two bolted to the floor of the Housing and one to a wall (Fig. 49). The other end of this module rests in roller module. bearing pin-sockets in the supported end of the next Thus each 40-foot joint can expand, be raised, be lowered, be moved to one side, or be rotated. In order to be able to determine modules, . the relative straightness a beam of optical light is used as a reference. light is transmitted from one end of the accelerator - 98 - of all 240 such This beam of optical to the other. The accelerator RETRACTABLE FLEXIBLE / FRESNEL. 3-INCH THICK TARGET . PIPE n-*-r FIG. 48--Each 40-foot-long accelerator girder is loosely coupled to the next with a flexible bellows arrangement. JPPDRT GIRDER --‘i4gDlAtKTER PIPE,40' LONG INTERCONNECTING FIG. 49--One end of each 40-foot long girder rests upon three adjustable worm-screw supports. pipe itself could not be used to transmit diameter would produce diffraction the mechanical alignment monitoring pipe’s primary function. this light beam, first because its small effects in a beam of light, and second because devices needed would burden the accelerator - 99 - -- .-_. ..m--*- -- ---* -_-- -,----..-....- .-...__c.__I It was decided to utilize mission of the reference the two-foot-diameter support girder for the trans- optical light beam. Visible light from a gas laser “point” light source is admitted to the 24-inch pipe at one end of the two-mile-long sembly. An observation system is located at the other end of the assembly, astwo miles away. Near each 40-foot coupling point and support set, an etched grating target plate is housed inside the 24-inch pipe (Fig. 50). This target is hinged at r^-. -1” A.. .-... 1. u .*: c: . ..,r 4 ‘: / 1. ,/’ * _ t P ii 4 ,“ m’ -* . . _ -...-_~..~~,~* F. .s -1 I, i ; ‘; .? .L . ‘,C ; . .--v ** -8 w ll,, ‘11.11,. .::::“’ r * \ .- i 1 -_ . .) 1. ’ i .yrwur- I FIG. 50--A retractable Frcsncl zone plate target is housed within each 40-foot-long girder to intercept the laser light beam and provide ali&mment indication. -100 .-,.1^ ~LIpII-l--_^,. .-. -*--...-._ the top and is normally stowed in a horizontal position. way, this target can be swung into the vertical light beam. Observation the grating at that point. supports under that target, by-step position By dropping alignment is under- in the path of the laser of the diffraction-interference in the path of the light provides the accelerator When alignment phenomena produced by minute indication of the alignment of one target at a time and adjusting the of the accelerator is achieved in a step- fashion. The above procedure aligns all the girders ator tube sections themselves in the accelerator. have been previously The acceler- optically aligned to the gir- an electron beam must be per- ders during assembly in the laboratory. I. Vacuum System In order to perform its function unimpeded, mitted to travel through as good a vacuum as possible. residual beam. gases in the way would result in collisions, For instance, accelerating Air molecules radiation, and other and a degraded the electron beam inside the klystrons which amplify the -8 radio waves passes through a vacuum of 10 mm Hg. This vacuum is pumped in the klystrons after manufacture nently sealed against the incursion down in a klystron, of air. and then the klystrons are perma- In fact, one of the causes of break- as in any vacuum tube, is outgassing from the materials inside the tube. For the same reasons, ated. However, . difficult the interior this four -inch-diameter, of the accelerator two-mile-long to evacuate and to maintain under the required 10m6 mm Hg. For this reason the accelerator once a vacuum is attained, must also be evacucylinder is a little more vacuum of better than is continuously pumped; that is, the vacuum pumps are kept pumtiing to keep removing airs and gases which might appear inside the tube. - 101 - To accomplish this, the accelerator has been divided into 30 sectors, The 30 subsystems served by an independent vacuum subsystem. nected only via the open accelerator just one of these thirty manifold, The following are intercon- paragraph describes subsystems. Alongside the accelerator drical itself. each itself, there extends a five-inch-diameter cylin- 330 feet long (Fig. 42). This manifold exhausts the accelerator by tapping into it at each ten-foot evacuates both the accelerator from the klystrons, rf feed point. Air drawn from these points thus and the waveguides delivering all of which comprise a continuous vacuum envelope. Air drawn into the vacuum manifold at these points is carried Gallery via four 8-inch-diameter the radio energy cylindrical “fingers, upstairs to the Klystron ” spread roughly equally apart. These four fingers then exhaust to an 8-inch-diameter drical manifold running along the sector of the Klystron horizontal Gallery cylin- (Fig. 47). This manifold is also connected to the rf output waveguides above each klystron to aid . in the evacuation of the system at this upper reach. Four getter-ion type vacuum pumps, rated at 500 liters per second and 10 -9 mm Hg at their input ports, exhaust this manifold to air. The getter-ion pumps begin their pumping after a portable rough pumping -3 -4 system has evacuated the accelerator down to between 10 and 10 mm Hg. This same rough pumping system is also used to re-evacuate the connecting waveguide between the output window of a newly replaced klystron porily valved-off waveguide of the accelerator The 24-inch-diameter alignment girder system. Gallery , connected to the girder a vacuum in the alignment.passage , must also be evacuated so that the laser beam will not be degraded by refraction. Klystron and the tem- A set of vacuum pumps in the interior via a 24-inch pipe, maintains of about 100 microns. - 102 - ml ___ __c _Cb_-___._I..__ _ “--“- . . ..- ‘-~~-..~ey-.e-e”~~e~e~ -.‘-‘I -FILeI”.“, -_----- -’ .‘.. . _ - .(_.__l___- ..- . -,p.w.mY ..“.e+.*-... Ml”.+--.’ A separate -4 power is used in the accelerator great deal of heat in the components through which it passes. inside each lo-foot dimensional change temperature and contraction accelerator Three areas in of the accelerating stability. through the booster klystrons and the high power klystrons, .’and through the penetrating must arrive the bunching of electrons. at the accelerator in the proper phase to match this. power as the internal and arrive at an improper in each klystron klystron changes, the radio waves phase. must dissipate as much as 74 kilowatts electron beam terminates this heat were allowed to build up, the collector at the collector. 70 independent water cooling subsystems have been installed Gallery. of If would become damaged. To remove the heat from these components before temperatures up, is Should the lines and waveguides carrying the radio waves change dimensions with temperature The collectors waveguides down to The radio wave through each high power klystron adjusted to accomplish will change velocity the natural expansion changes would violate the require- The radio waves from the master oscillator, the accelerator, of an inch, in radio wave. If these sections because of varying heat dissipation, of copper under temperature ment for dimensional pipe section must be held to some to within 50 millionths tolerances, order to control the velocity carefully and generates a are sensitive to this power dissipation. The cavities very strict of Control System A great deal of electric particular therein mm Hg. Temperature J. above the beam switch- a vacuum in the many large vacuum chambers yard to maintain about 10 system has been installed vacuum . can build in the Klystron Each of these subsystems includes a return header to receive heated - 103 - water from the cooled components, flow as necessary, to purify the water, temperature transfer a surge tank to supply extra water for smooth a pump to circulate a heater’ to permit if necessary, the water, a filter and a demineralizer heating of the water to the initial a heat exchanger to permit cooling of the water by of heat to a second water system feeding a cooling tower, valve to control the temperature design of the water to be resupplied a blending to the components, and a supply header to feed the supply lines (Fig. 51). FROM MAKE-UP WATER DISTILLATION PLANT 1 TO ONE OF TWO COOLING TOWERS - I SURGE TANK r---DEMINERALIZER -! - 1 I I HEAT I IEXCHANGER I I L----J SUPPLY HEADER - 3-WAY CONTROL VALVE 49,~314 FIG. 51--Typical block diagram of one of the 70 closed-loop recirculating water systems for the accelerator and its components. 1 The heater is not included in the water subsystems controlling temperature. - 104 - klystron On the south side of each sector of the Klystron Gallery, an equipment alcove has been built to house these components of these subsystems. Each of these 30 sector alcoves contains one of these water subsystems to supply cooling water to the accelerator . inal temperature section water jackets (Fig. 41) in that sector at a nom- of 1lO’F f 0.2’F Each of these 30 sector but adjustable over the range of 95’F to 120’F. alcoves also contains a second of these water subsystems to supply water at 112’F f 1°F to control the temperature of the rf lines and waveguides in that sector. Every third sector alcove also contains a third such water subsystem. subsystem supplies cooling water to the 24 klystrons sectors to maintain klystron temperature This in the associated three no higher than 158’F. Thus 20 of the sectors contain two water subsystems and 10 of the sectors contain three. The water system is the double closed-loop the cooled components is treated, restored type. Water brought up from to temperature, and returned components to repeat the job. “The-heat from this water is transferred shell-and-tube via a heat exchanger to a second loop of water which circulates an external cooling tower and back. There are two cooling towers, to the through one serving all the subsystems in the eastern half of the machine and one serving the western half.’ Some water will be lost from these systems due to natural evaporation, leakage, etc. Make-up water to each surge tank is supplied from a distillation plant on the site which in turn is supplied by thelocal metropolitan K. Electrical water system. System When the accelerator over a temporary was under construction, 60,000-volt transmission 1 it was supplied electricity line. After beam turn-on ’ and in There are two more cooling towers at SLAC, one serving a water system in the laboratory buildings and one serving the beam switchyard and end station area. - 105 - order to operate the beam at its full capabilities, more electricity was required than could be supplied by that line, as much as 80,000 kilowatts. experiments In addition, with the beam become more complex in years to come and larger experimental it is estimated that eventually apparatus is required, 300,000 kilowatts of electric line has been constructed as much as power may be required. To supply this electricity, a very high voltage (220,000 volts) transmission to a nearby high capacity transmission power line has been constructed using a relatively line. This new design of pole structure, single tubular poles averaging seventy feet high and painted to match the landscape (Fig. 3-wire 52). Because this new type of pole is capable of bearing only one circuit, the original as instead of the two carried temporary 60,000-volt by conventional four -legged towers, line is being retained to supply emergency power in case of an outage on the main line. ~~~,Tyw:--~~ -~---.----aw !: ‘V _ ..,‘c? c .’ F ” i. i>, p-’ . ;j B t* h i i ; L i. t: ; ; 1 i : -yy?-T w. ‘5, ii .;<J : ‘, ’ .I : 6-- f .’ . .-._ 1 ..- ---7 ’ 4I ‘. ‘, \. ’ ii. : <1 t. $ .i 1’ I .- A\/f”.. ,.I’ ,.:‘r;.’->)i7 -4‘t \ “2’ / my&.e_&:, I 1 { , 1 II ,,I ..i . : i 4 FIG. 52--One of the pole structures in the SLAC highvoltage transmission line. - 106 - This high voltage power is brought to a substation near the output end of the accelerator, where its voltage is stepped down to about 12,000 volts for distribution over the site. L. Instrumentation All these distribution lines have been placed underground. and Control Along the north side of the Klystron Gallery, at each of the 30 sectors, alcove has been built to contain various instrumentation that sector. In this alcove, in the sector are made. ing adjustments initial ation of the accelerator, and control devices for setting up and adjustments Also here, from time to time, can be performed. However, maintenance and operat- in normal satisfactory and control information tors steady oper- is transmitted Central Control Building near the east end of the accelerator. ing remotely. of the components these control alcoves will not be manned. All essential instrumentation control of the accelerator an and the beam switchyard In case of necessity, &d maintenance personnel to-Klystron Monitoring are performed the engineer-in-charge and in this build- can dispatch opera- Gallery sectors requiring Thus the operation of the entire machine is supervised to a attention. from the one control point. The job of the people in this building is to assure that the proper desired beam is delivered to the end station area. - 107 - IXII. USING THE ACCELERATOR The beam from the two-mile and enters a lOOO-foot-long machine exits at the east end of the accelerator “beam switchyard” yard is an extension of the underground horizontal Accelerator plane as the end of the Housing. to any of selected research areas, processing Housing and lies in the same In order to direct the accelerated the beam switchyard toward its output end. In this beam switchyard, direct the beam into experimental (Figs 4 and 53). The beam switch- gradually becomes wider huge electromagnets process and areas located in two target buildings. of a curved electron beam results motion of a linear beam, the beam switchyard in more radiation beam Because than does the is covered with 40 feet of shielding earth and concrete. - , i I G . - .. .._- . FIG. 53--The research end of the accelerator. The fork-shaped beam switchyard, under 40 feet of earth shielding, directs the accelerator beam to the desired experim,ental area in the two end station target buildings. - 108 - The larger of the two target buildings is a single room with 25,000 square feet of floor space. Its concrete walls are over 70 feet high, It is in these two target buildings, and in an auxiliary that the results of directing 20-acre open area behind these buildings, the electron beam on a nuclear target are studied. . When a high energy electron is caused to travel through some target material and passes within nuclear dimensions of a target nucleus, one of two things . can happen. An electromagnetic interaction between the electron and the nucleus can cause the electron to veer off in its path at some angle while the interacting nucleus recoils at a different angle. This phenomenon is called “elastic ing. ” The other thing that can happen is similar some of the kinetic energy of the bombarding different elementary particles scatter- except that during the interaction, electron is lost and some new and eventually emanate from the point of interaction. This phenomenon is called “inelastic scattering. ” of the two target buildings, End Station B, was designed to . in the analysis of the “secondary” particles produced from such in- The smaller specialize elastic interactions. In this target building, the accelerated used to produce secondary beams of new particles variety - of secondary particles approaching electron. for observation The quantity of secondary particles barding beam. The Stanford two-mile . produced in a given (the current) in the bom- beam is unique in the combination of these Its 20-GeV electrons have three times the energy of those from the next highest energy electron accelerator. The beam current is 300 times higher. , In light of these advantages, some of the first of the two-mile and study. The created in this way depends upon the energy of the time depends in addition upon the number of electrons two parameters. electron beam is experiments planned for use beam involve creation and study of secondary particles. stance, in one series of experiments For in- the electron beam will bombard a thick - 109 - copper target at the entrance of End Station B. The interactions will cause all kinds of secondary particles direct these into a separation to be produced. to be much like an electron only heavier. into a cylinder assembly. Magnet systems will system which will stop all particles kind called “muons. I’ The muon is a short-lived directed in the target except one secondary particle The resultant of liquid hydrogen surrounded which appears muon beam will then be by a large spark chamber The spark chamber assembly itself is contained within a gigantic 200- ton electromagnet. When the muons approach the hydrogen nuclei, and are scattered off in all directions. the spark chamber, As these scattered they create high-voltage gies. muons pass through lightning-like along their paths which can be photographed. curve the path of the scattered they produce interactions discharge The surrounding sparks magnet serves to muons by an amount which depends on their ener- Analysis of the photographs ledge of both the direction of the curved trajectories thus provides know. of motion and of the energy of the scattered particles. This in turn leads back to further understanding and the hydrogen nucleus responsible of the interaction for the scattering. Some of the same apparatus is used to investigate the possibility panying the muons there are other as yet unknown elementary are similar to the muon, differing from the University aimed at the achieving, made up exclusively of particles “strange” The University particles. 72-inch-diameter that accom- particles which perhaps only in mass. Another team of experimenters investigation of the muon of California by special separation known as K-mesons, of California bubble chamber for installation plans an processes, of a beam one of the family of is modifying . and enlarging in this K-particle K-mesons pass through the liquid hydrogen of the bubble chamber, beam. its As they leave - 110 - ---V -a*cI -...--- --13.-C-,. -*. _ _x_______,- - .___-..- -.- -.-.- xII-w”-. ..,--w-e.. _ _ “_I I. Similar tracks are produced by other particles behind fine tracks of bubbles. the K-meson suffers a violent collision Photographs of with a hydrogen nucleus. these bubble tracks then give a graphic record of the nuclear event. AndysiS millions of such photographs provides leading to further processes, detailed information understanding if Of about the interaction of the K-meson and.its progeny. SLAC is building another bubble chamber to be installed behind End Station B to receive a beam of high-energy study the interactions x-rays between x-rays produced by the electron beam and to and the nuclei of the hydrogen in this bubble chamber. Other research urements to be carried out with the new accelerator of nuclear size and structure at Stanford with the University’s this analysis, the larger carried will extend meas- out during the past fifteen years 300-foot-long, l-GeV of the two target buildings, To perform Mark III. End Station A, is equipped The largest of the three is over 150 feet long . and weighs over 3000 tons. These spectrometers can be swung around an axis with three huge spectrometers. and are set at various angles from the line of the bombarding accept particles scattered at particular then separate out all particles tric charge. identified By electronic beam in order to angles. Magnets in the spectrometer except those having a particular means, particles of a particular energy and elec- energy are then with respect to their mass. The result in each spectrometer of the number of particles of a unique kind scattered The three spectrometers ranges of scattering energies. analyzing many scattering of an interaction are of different is a tally at a unique angle. sizes and thus cover different With these three each covering a wide arc and , angles successively, can be obtained. In the process a complete picture of the results of elastic scattering, the electrons scatter off at each angle with a unique energy for that angle. This energy, - 111 - which of course also depends upon the energy given the electron by the accelerator, can be calculated. In inelastic scattering, creation of other kinds of particles, means that inelastically at a particular scattered because energy has gone into total interaction electrons energy is reduced. can have different This amounts of energy angle and that those energies are always less than the energy of an elastically scattered electron. Setting a spectrometer with elastic scattering to receive only particles provides a spectrometer to discriminate tering provides information the scattered electrons having the energy permitted data for understanding that kind of action. againstparticles about the inelastic having the energy of elastic scatscattering process. Not only can be studied, but so can the secondary particles In the study of elastic scattering, Setting produced. in order to be able to relate the experimental results just to the characteristics of the little-known nucleus and not to those of the better understood electrons, beam of positrons, the process will be repeated using a which are electrons of positive charge. To do this, a “positron source” has been placed in the path of the two-mile about one-third of the way down the machine. third of the accelerator strike emanate from inelastic collisions then accelerated high-energy spectrometers parison a target. accelerated are The resulting to the target in End Station A and the the elastic scattering to separate the experimental of the positrons. Corn-- of electrons effects of the bombarding . per particle effects of the nucleus being studied. Not only will large spectrometers resulting which These positrons of the accelerator. of this data with that obtained from elastic scattering from the experimental in the first Among the secondary particles two-thirds positron beam is delivered mits the scientist particles Electrons there are many positrons. down the remaining are set to monitor electron beam at a point from inelastic be used to study the yield of secondary but also a huge spark chamber is collisions, - 112 - _-_. I __-_,__-___ .*-_...“. -” . ___.* ___ _ _--_- “nl_.. .--..- - .-,.------..-.” being constructed thin metallic x-rays for similar By directing purposes. sheet, a copious beam of high-energy the electron beam into a x-rays is produced. will be directed to a gaseous hydrogen target cylinder The x-rays special spark chamber. interact located inside the with the hydrogen nuclei and produce violent events from which emerge several secondary particles. secondary particles emanate from the collision spark chamber leaving momentary As these target they spread through the visible lightning-like tracks. are used to photograph these tracks in three dimensions, presentation These Three cameras resulting in a stereo of the complete interaction. These are just a few of the types of experiments planned for the new accelerator for the first year of its use. Scheduling cannot be done much more than a “Elementary year in advance. particle year new discoveries mean re-oriented of newer experiments previously One of the excitements physics” is still in a dynamic state. Each thinking. not imagined. of accelerator development, often turned out to be the most dramatically about at the time of their original and probably all life sciences, Of phys its. effective As Professor particle have physics stands W. K. H. Panofsky, Center, has said, “All must ultimately many accelerators in areas not even known Elementary conception. of man’s knowledge. of the Stanford Linear Accelerator particle the design of this new science is that the future is so unknown. Throughout the short history at the frontier This in turn requires Director other physical sciences, rest on the findings of elementary It would indeed violate all our past experience in the progress science if nature had created a family of phenomena which governs the be- havior of elementary particles without at the same time establishing between these phenomena and the large-scale very particles type of structure any links world which is built from those . . . . . We cannot afford to be ignorant of the most fundamental on which everything else depends. ” - 113 - ‘F----y _. _. _ _” I -_______ ~~-~~~~=~.~‘~~~~~~1.~‘~~~ - : -. _.-. .___I.-.,_.. -. . . .,- .._. --.-.“-M .I ._ -___1 . - . . . . _ .._ X.~..-- ---.1-- ,___1_1. APPENDIX I SIAC CHRONOLOGY April 1957 Proposal for two-mile accelerator University to Federal Government submitted by Stanford September 1961 Project April Contract signed by U. S. Atomic Energy Commission Stanford University 1962 authorized by U. S. Congress and July 1962 Ground breaking; July 1964 Start of accelerator October 1, 1965 First “Users Conference, I* attended by 150 people from laboratories all over the world, to be made acquainted with SLAC. December 1965 Installation February Program Advisory scheduled the first two-mile beam 12, 1966 construction begins installation of accelerator complete Committee met, and approved and experiments to be performed with the May 21, 1966 First beam transmitted the accelerator June 2, 1966 18.4 GeV of beam energy achieved June 22, 1966 Second “Users July 13, 1966 Positrons October 1’7, 1966 First interlaced multiple intensities accelerated November 1966 Experiments January 10, 1967 20.16 GeV of beam energy achieved over entire two-mile length of Conference” held at SLAC accelerated beams of different energies and begin with the beam in the end stations - 114 - APPENDIX II GENERAL SLAC ACCELERATOR Accelerator SPECIFICATIONS 10,000 feet length 10 feet Length between feeds Number of accelerator sections . 960 Number of klystrons 245 Peak power per klystron 6-24 Beam pulse repetition l-360 rate MW pps RF pulse length 2.5 psec Filling 0.83 psec time Electron energy, unloaded 11. 1 - 22.2 GeV Electron energy, loaded 10 - 20 GeV Electron peak beam current 25-50 Electron average beam current 15 - 30 /JA Electron average beam power 0.15-0.6 mA MW Electron-beam pulse length 0.01 - 2.1 psec Electron-beam energy spread (max) f 0.5% Positron energy 7.4 -14.8 Positron average beam current 1.5 PA GeV Multiple -beam capability 3 interlaced beams with independently adjustable pulse length and current Operating frequency 2856 MHz Operating 24 hours/day . schedule -115 - 4 APPENDIX HIGH ENERGY PARTICLE III ACCELERATORS Birmingham, England Cosmotron, Brookhaven, New York Saturne, Saclay, France Princeton-Pennsylvania Accelerator, Princeton Bevatron, University of California ITEP, Moscow, U.S.S.R. NIMROD , Harwell, England JIM, Dubna, U.S.S.R. ZGS, Argonne, Illinois *CERN, Switzerland *AGS, Brookhaven, New York *Serpukhov, U.S.S.R. Electron 1 3 3 0.001 0.032 0.005 3 6 7 8 10 12 28 33 70 0.180 0.160 0.001 0.080 0.001 0.024 0.064 0.080 0.048 Synchrotrons 6 6 10 0.5 0.5 1.0 Linear Accelerators Mark III, Stanford Orsay, France Kharkhov, U.S.S.R. SLAC , Stanford . 0.03 0.02 0.10 0.01 0.03 0.6 1.0 0.4 1.1 1.2 1.3 1.5 2.2 2.3 4 6 Frascati, Italy Lund, Sweden Tokyo, Japan California Institute of Technology _ Cornell University, New York Bonn, Germany NINA, Daresbury, England *DESY, Hamburg, Germany *Cambridge Electron Accelerator, Massachusetts *Yerevan, U.S.S.R. *Cornell University, New York Electron Average Current (microamperes)** Beam Energy (GeV) Proton Synchrotrons 3 2.4 1 30 1.2 1.3 2 20 *Alternating gradient synchrotrons **Numbers rounded off - 116 - -=w.. -?.I-*.. a .“.,._ _>,.,. ,I ._,- _,__.. ---l_.____l--. _““. -..x..-_ ,_.._... - _ _._ .- .I._ --.I r-...-.-l----l*-\---w-. .._ .._a-. L.-..--X-.-I~..‘a-. -~_-x-I---II--yII.u.“~.~ __l_n-.-1____. I ” .._.. _I- )..m. BIBLIOGRAPHY Books Borghi, 1. R. P. , --et al. , “Design and Fabrication of the Accelerating Struc- ture for the Stanford Two -Mile Accelerator, ” in Advances in Microwaves, ed. L. Young (Academic Press, 1966). : . . 2. Ford, K. W. , The World of Elementary New York, 3. Heckman, H. H. and P. W. Starring, (Holt-Rinehart-Winston, Livingston, Panofsky, Wilson, Co. , Englewood Cliffs, Nuclear Physics and the Fundamental New York, M. S. and J. P. Blewett, W. K. H. , “Particle Science-and Technology 7. Publishing 1961) . Book Company, Inc., New York, 6. (Blaisdell G. Gamow , The Atom and Its Nucleus (Prentice-Hall, Particles 5. Particles 1963). New Jersey, 4. New York, Particle Accelerators (McGraw-Hill 1962 ). ” MC Graw -Hill Accelerator, (McGraw-Hill Encyclopedia Book Company, Inc. , New York, R. R. and R. Littauer , Accelerators: (Doubleday-Anchor 1963 ) . of 1960). Machines of Nuclear Physics Books, Garden City, New York, 1960 ). Journal Articles 1. L. W. , -et al. , “Berkeley Alvarez, Scientific Instruments 2. Becker, 2, Proton Linear Accelerator, 111 (1955 ). G. E. and D. A. Caswell, “Operation of a Six-MeV Linear ” Review of Scientific Instruments tron Accelerator, i . 3. Chodorow, M. , -et al. , “Stanford High-Energy (Mark III), ” Review of Scientific Instruments 4. ” Review of Elec- -22, 402 (1951). Linear Electron Accelerator -26, 134 (1955 ) . “Contractor Casts 2-Mile Tunnel With 80-Foot-Long Engineering News Record 172, 82 (June 18, 1964 ). Ganged Forms,” - 117 - _ ..L __ )_ *.s.e. I%,C, “.“,*wle‘“” ~‘“**IC~~~r7ww7.7..-r ” -* I ,_ . _ - “v.“rsras.wse.vcQ.w~~~,~~ .I_“_p-m ., .- -._. I -._-. 5. Dupen, D. W. , “SLAC ‘s Tiny Universe, ” Stanford Review LXVI (No. 2), 18 (1964 ) . 6. Dupen, D. W. , “Stanford’s 7. Ginzton, E. L. , W. W. Hansen, and W. R. Kennedy, “A Linear ” Review of Scientific Accelerator, 8. Ginzton, Scientific 9. Long, Long Beam,” New Scientist 30, 296 (1966). E. L. and W. Kirk, American Instruments “The Two-Mile Electron -19, 89 (1948 ) . Electron Accelerator ,” 205, 49 (November 1961). “High Energy Accelerators ,” Atomics Magazine, Vol. 15, No. 3 (1962)) Vol. 16, No. 3 (1963), and Vol. 17, No. 4 (1964 ). 10. Neal, R. B., “Design of Linear Electron Accelerators With Beam Loading,” Journal of Applied Physics 29-, 1019 (1958 ). 11. “Chaotic Page, B. M. and L. L. Tabor, Structure Cenozoic Rocks Near Stanford University, and Decollement California, in ” Bulletin of the Geological Society of America -(in press ) . 12. Panofsky , W. K. H. , “Experimental Techniques, ” Springer Tracts in Modern Physics 39, 138 (1965). 13. Post, R. F. and N. S. Shiren, “The Stanford Mark II Linear Accelerator,” Review of Scientific 14. Instruments 26, 205 (1955 ) . Rose, B. F., ” Atom Smasher for Nuclear Physics Research, ” Military Engineer 56, 2 (1964 ) . 15. “Stanford Linear Accelerator, 64 (February 16. Varian, ” W ’estern Construction Magazine -39 (No. 2), 1964 ) . R. H. and S. F. Varian, “A High Frequency Oscillator and Ampli- fier ,” Journal of Applied Physics 10, 321 (1939 ). 17. Wilson, R. R. , “Particle Accelerators (March 1058). - 118 - ,” Scientific American 198, 64 ’ . Conference Proceedings 1. . 2. . J. , --et al. , “Status of Design, Construction, Ballam, at SLAC , *’ Proceedings, Fifth International Accelerators, Italy, Frascati, Enerffy Accelerators 3. Proceedings 4. 5. Loew, . Techniques, ‘* Proceedings, Washington, 1961). IEEE D. C. , March 10-12, 1965. Center ,I* MURA, Madison, Wisconsin, July 1964. 1964 Linac Conference, Symposium, Washington, Report on the Stanford Linear Accelerator Neal, R. B., **The Two-Mile Anniversary Office, of a High Power Pulsed Klystron,” Alignment Conference, ‘*Progress G. A., Proceedings, 6. W. B. , “Linac Accelerator Conference on High- 1584 (1953). of the I. R. E. 41 -’ Hermannsfeldt, Particle Printing M. , “Design and Performance Chodorow, 1965. of the 1961 International (U. S. Government Programs Conference on High-Energy September 9-16, M. H. , Proceedings Blewett, and Research Linear Accelerator,” Georgia Institute - Proceedings of Technology, of the 75th Atlanta, Georgia, 57 (1963). 7. Neal, R. B. , “The Stanford Two -Mile Linear Accelerator, American Vacuum Society Symposium, Chicago, Illinois, *’ Proceedings, September 30 - October 2, 1964. 8. Merdinian, G. K. , J. H. Jasberg, and J. V. Lebacqz, manent Magnet Focused , S-Band Klystron Prodeedings , 1964 Electron October 29-31, 9. Miller, for Linear Devices Meeting, “High Power, Accelerator Washington, Use. ** D. C. 1964. R. H. , R. F. Koontz and D. D. Tsang, “The SLAC Injector, Proceedings, Per- IEEE Particle Accelerator March 10-12, 1965. - 119 - Conference, Washington, ** , D. C. , “Construction Osgood, E. W. and J. M. Keith, 10. at the Stanford Linear Accelerator Concrete Institute of the Accelerator Housing Center ,” Presented at Annual American Convention (1965 ) . . Reports Atchley , F. W. , “Preliminary 1. Geological Investigation Felt Lake Linear Accelerator Sites, Stanford University,” to John A. Blume and Associates DeStaebler, 2. H. , “Average Radiation Levels Inside the Accelerator Stanford University, DeStaebler, 3. 4. H. , “Radioactive California (1962). Center, Stanford University, Stanford, - H. , “Transverse Accelerator, ” SLAC Report No. 9, Stanford Linear Accelerator Radiation Shielding for the Stanford Two-Mile Stanford, Site Investigation Aetron-Blume-Atkinson 6. Stanford Linear Accelerator DeStaebler, “Geologic California for Stanford Linear Accelerator Report No. ABA-88 Laboratory, Center, (1962). Center, ” (1965). Neal, R. B. , “A High Energy Linear Electron No. 185, Microwave When Gas in the Tunnel, ” SLAC Internal Report, (1962). Stanford University, 5. Report, Stanford, Stanford Linear Accelerator California Private Report (1960 ). The Machine is Off, ” SLAC Internal Center, of the Sand Hill and Accelerator, Stanford University, ” M. L. Report Stanford, California (1953). 7. Neal, R. B. , and W. K. H. Panofsky, “The Stanford Mark III Linear Accel- erator and Speculations Concerning the Multi-BeV Linear Accelerators, atory, Applications of Electron ” HEPL Report No. 80, High Energy Physics Labor- Stanford University, Stanford, California (April 1956). - 120 - ll--l-.“>%l --.- ~m”_Cs.e,x..s,~s,“Y*..Y~-~.~,~% ..I. -I--_ _ .*- . .- -..II--s.s>--T.^.-.P --*-- ___yl--- I-- -, 8. Trask, P. D. , “Engineering Geology, Proposed Linear ator Sand Hill Site, Stanford University,” Electron Acceler- Private Report to Aetron-Blume- Atkinson (1961). Government Documents 1. the Atom, ” (U. S. Atomic Energy Commis.- : “Understanding Accelerators sion, Division of Technical Information Extension, Oak Ridge, Tennessee, 1963). 2. Background Information posed Stanford Linear on the High Energy Physics Program Electron Committee on Atomic Energy, ment Printing 3. Accelerator Project, and the Pro- Report to the Joint Congress of the United States (U. S. Covern- Office, Washington, D. C. , 1961). Report of the Panel on High Energy Accelerator Physics of the General Advisory Committee to the Atomic Energy Commission and the President’s Science,Advisory Committee, TID-18636 (U. S. Atomic Energy Commission, Division of Technical 4. Information, Stanford Linear Accelerator Washington, D. C. , April 26, 1963). Hearings Before the Subcommittee Center, on Research and Development and the Subcommittee on Legislation Joint Committee of the Congress of the United States, July 14 on Atomic Energy, and 15, 1959 (U. S. Government Printing Office, Washington, D. C. 1959). i - - 121 - T. . ._ _1-. -7-e- ~--“---,. _...-.. __-,.-.,-1..___ - .““.._ .* ,,.,d,-ae -..(. --“~ls _“._._ .‘ ..~^-_ _.-. m.eaTe- --.- IL_r _.-_ _..~.“.___I____ W.-l.. .-__.“.-“-e--.m,wq ---*.- . . . . -.. INDEX ABA, 57 Acceleration system, 82ff Accelerator tube fabrication, 83ff Accelerator tube tuning, 87 Accessways, 80 Aetron-Blume-Atkinson, 57 Alignment requirements, 70,71 Alignment principle, 98ff Alternating gradient accelerators, 24ff Alternating gradient focusing, 25 Alvarez, L., 30,32 Argonne National Laboratory, 24,25,54 Atomic Energy Commission, 4, 25,54,56 Barber, W.C., 52,55 Beam guidance, 97 Beam switchyard, 3,108 Betatron, 17,24 BeV, 21 Bevatron, 33 Bloch, F., 55 .’ British Atomic Energy Establishment, 33 Brookhaven National Laboratory, 24,25,33 Bubble chamber, 110,111 Cambridge Electron Accelerator (CEA) , 25 California Institute of Technology, 21 Chodorow, M., 44,55 Cockroft-Walton generator, 12 Concrete, housing, 73ff Constant gradient design, 86 Contract 400, 58 Cosmotron, 24 Cyclotron, 13 Cyclotron, AVF, 26 . Drive system, . ----.. m.#.- “. .._-_ -___ _.“._. Fabrication, accelerator France, 24 Frascati, 21 tube, 8 3ff GeV, 21 Germany, 25,29 Ginzton, E.L., 37,44,49,55 Geology, site, 56 Guidance, beam, 97 Hansen, W. W. , 34ff, 50 Harwell, 33 Heavy ion accelerators, 30,33 High energy physics, 5 Hofstadter, R., 50,52,54 Housing construction, 66,7Off Injector, Mark HI, 51 Injector, SLAC, 89 Instrumentation and control, Interlaced beams, 95 Ising, G., 29 Italy, 21 107 Kerst, D. W., 17 Klystron, 4Off, 82,91ff Klystron window, 93 Lawrence, E. O., 13 Linear accelerators, 28ff McMillan, E. M., 19,21,23 Magnetron, 30,37,40 Mark I, 37ff Mark II, 45,50 Mark ILI, 46ff, 60,86,111 Mark IV, 54 96 Earth’s magnetic field, 97 Earth movement, 69 Earthquake faults, 68,69 ‘%-ES‘+, Eisenhower, D. , 57 Electrical system, 105 Electron gun, SIAC, 90 Electron linear accelerator, 34ff Electron-volt, 11 Electrostatic accelerators, 11 Elementary particles, 5ff, 110 Elementary particle physics, 113 End stations, 109 England, 30,33,36,44,54 -122 - -. .x . - . ._ __._” .~.~~~~~s~~--~M .--- -.r.- r”.“..--I._--..- -..---~-..~-.-*- ,, e,,-.“*C.UI INDEX Eisenhower, D., 57 Electrical system, 105 Electron gun, SIAC, 90 Electron linear accelerator, 34ff Electron-volt, 11 Electrostatic accelerators, 11 Elementary particles, 5ff, 110 Elementary particle physics, 113 End stations, 109 England, 30,33,36,44,54 ABA, 57 Acceleration system, 82ff Accelerator tube fabrication, 83ff Accelerator tube tuning, 87 Accessways, 80 Aetron-Blume-Atkinson, 57 Alignment requirements, 70,71 Alignment principle, 98ff Alternating gradient accelerators, 24ff Alternating gradient focusing, 25 Alvarez, L. , 30,32 Argonne National Laboratory, 24,25,54 Atomic Energy Commission, 4, 25,54,56 Fabrication, accelerator France, 24 Frascati, 21 GeV, 21 Germany, 25,29 Ginzton, E.L., 37,44,49,55 Geology, site, 56 Guidance, beam, 97 Barber, W.C., 52,55 Beam guidance, 97 Beam switchyard, 3,108 Betatron, 17,24 BeV, 21 Bevatron, 33 Bloch, F. , 55 .’ British Atomic Energy Establishment, 33 Brookhaven National Laboratory, 24,25,33 Bubble chamber, 110,111 Hansen, W. W. , 34ff, 50 Harwell, 33 Heavy ion accelerators, 30,33 High energy physics, 5 Hofstadter, R., 50,52,54 Housing construction, 66, 70ff Injector, Mark III, 51 Injector, SLAC, 89 Instrumentation and control, Interlaced beams, 95 Ising, G., 29 Italy, 21 Cambridge Electron Accelerator (CEA) , 25 California Institute of Technology, 21 Chodorow, M., 44,55 Cockroft-Walton generator, 12 Concrete, housing, 73ff Constant gradient design, 86 Contract 400, 58 Cosmotron, 24 Cyclotron, 13 Cyclotron, AVF, 26 . Drive system, Lawrence, E. O., 13 Linear accelerators, 28ff McMillan, E. M., 19,21,23 Magnetron, 30,37,40 Mark I, 37ff Mark II, 45,50 Mark III, 46ff, 60,86,111 Mark IV, 54 96 - -e--m. -7 I.- .._-_ ---_ 107 Kerst, D.W., 17 Klystron, 4Off, 82,91ff Klystron window, 93 Earth’s magnetic field, 97 Earth movement, 69 Earthquake faults, 68,69 +Tw-e-. tube, 83ff 122 - .._. r _.-. 1 - .-I.,__~__ ..w..*r~~~~-*a”~~~~-~. -_ .._“- “.“.._-I.,- . .. . __-__.-- “l_lr ., II--- -a._*. Medical accelerators, 54 Modulator, SLAC, 95 Mrem, 60 National Science Foundation, Neal, R.B., 54,55 Office of Naval Research, Target buildings, 3,109 Technological spinoff, 89 Temperature control system, 103 Traveling wave principle, 36 Trigger system, 95 Tuning, accelerator tube, 87 56 39,45,46 Panofsky, W.K. H., 49,55,113 Phasing system, 96 Positron source, 112 Post, R. F., 46 Power line, high voltage, 106 Princeton University, 24 Proton linear accelerators, 30ff Pulse rate, 19 Pulse rate, SLAC, 95 University University University Radar, 30,40 Radiation effects, 60ff Radiation from electron beams, 59 Radiation shielding, 5 9ff Relativity, 16,19,22,26,51 Research area, 108 Research at SLAC, 108ff Resonant cdvities, 34 Rhumbatron, 34,42 Scattering, electron, 109 Schedule, 4 Schiff, L. , 54 Seaborg, Glenn T. , 7 Secondary particle production, Site geology, 68 Site, SIAC, 66ff Sterling, J. E. W., 56 Strong focusing, 25 Support and alignment, 98 Spark chamber, 110,112 Spectrometers, 111 Switchyard, beam, 3,108 Switzerland, 22,25 Synchrotron, electron, 20,23 Synchrotron, proton, 23 Synchrotron radiation, 27 Synchrocyclotron, 21,23 Synchrophasatron, 33 U.S.S.R., University 19,22,24,25,33 of California, 13,19,22,24, 30,33,56,110 of Illinois, 17 of Minnesota, 32 of Southern California, 32 Vacuum system, 101 Van de Graaff generator, Varian, Russell, 34,41 Varian, Sigurd, 40 Veksler, V.I., 19,21,23 Velocity modulation, 42 Water system, 103 Waveguide penetrations, Weak focusing, 24 Wideroe, R., 29 Williams, J. H., 32 -Window, klystron, 93 Woodyard, J., 31,37 12,32 82 ZGS, 25 109 A :, .,- m , - 123 - - w.I-‘-T ‘.-“.~.-rr - ._ .-.-.-^-._.I.-,_.- .;.- .-.. ~.wmlm*_..“.l--. ^. ._. ...___,.._I._. -.._--^_“%.” .“_&.-. “^-e.,m..--. I,~I~..-L..I~-~-~~P~..~iif**.~~~~-...~.‘, -.-_..--.,- 1 I---..“,“^_1 .,.... _“, _-__ __-..-. *( _l(, ,_._*-, -.- .^_. -. ^_ “.-s-c .%.” -...q...-*-m-c

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